packagefs: Remove support for HPKGv1.

The current version is "v2", and it has been since the final PM branch
was merged back in 2013, so it's unclear if anyone actually uses this
file format. The "package" command can still of course read these
files, it's just that packagefs will now not be able to.

It's very unlikely anyone is impacted by this change.

packagefs: UnpackingAttributeCookie: Open package

... when reading non-inline attribute data. Generally the package should
already have been opened by the PackageNode owning the attribute (in
InitVFS()), but that isn't the case for queries, which can read
attributes from entirely unsuspecting nodes.

Together with the QueryParser fix that should fix queries involving
non-indexed attributes.

packagefs: Fix attribute indexing

Since the package nodes' attributes are indexed before the VFS has
accessed any of its nodes, the package wasn't open and reading the
attribute data would fail. We do now open the package explicitly in
UnpackingAttributeCookie::IndexAttribute(). Moreover, as an
optimization, we also open the package in Volume::_AddPackageContent(),
so the package file isn't repeatedly opened and closed as its nodes are
being registered.

hpkg format: compress the whole heap

Instead of handling compression for individual file/attribute data we
do now compress the whole heap where they are stored. This
significantly improves compression ratios. We still divide the
uncompressed data into 64 KiB chunks and use a chunk offset array for
the compressed chunks to allow for quick random access without too much
overhead. The tradeoff is a limited possible compression ratio -- i.e.
we won't be as good as tar.gz (though surprisingly with my test
archives we did better than zip).

The other package file sections (package attributes and TOC) are no
longer compressed individually. Their uncompressed data are simply
pushed onto the heap where the usual compression strategy applies. To
simplify things the repository format has been changed in the same
manner although it doesn't otherwise use the heap, since it only stores
meta data.

Due to the data compression having been exposed in public and private
API, this change touches a lot of package kit using code, including
packagefs and the boot loader packagefs support. The latter two haven't
been tested yet. Moreover packagefs needs a new kind of cache so we
avoid re-reading the same heap chunk for two different data items it
contains.

packagefs: Add support for hpkg format V1

* Add union-like class PackageData which wraps the V1 and V2
BPackageData classes.
* GlobalFactory: Create a data reader depending on the data format
version.
* Package: Add a loader for V1 format and try that, if the other one
fails.

package kit: internalize BPackageDataReader

It is no longer public (or even private) API. BPackageDataReaderFactory
returns a BAbstractBufferedDataReader instead. The advantage is that
the latter doesn't have hpkg format specific dependencies.

packagefs: Share string instances globally

Introduce a class String which refers to shared private data that is
registered in a global hash table (in class StringPool) and use the
class consequently. This eliminates duplicate allocations for the same
string and also speeds up tests for equality. There's quite a bit
overhead for the management structures (apparently even more than for
the string data itself), but due to almost all strings being used
multiple times this still almost halves the memory usage for string
data.

packagefs: Organize sources into subdirectories

packagefs: UnpackingAttributeCookie: Open package

... when reading non-inline attribute data. Generally the package should
already have been opened by the PackageNode owning the attribute (in
InitVFS()), but that isn't the case for queries, which can read
attributes from entirely unsuspecting nodes.

Together with the QueryParser fix that should fix queries involving
non-indexed attributes.

packagefs: Fix attribute indexing

Since the package nodes' attributes are indexed before the VFS has
accessed any of its nodes, the package wasn't open and reading the
attribute data would fail. We do now open the package explicitly in
UnpackingAttributeCookie::IndexAttribute(). Moreover, as an
optimization, we also open the package in Volume::_AddPackageContent(),
so the package file isn't repeatedly opened and closed as its nodes are
being registered.

hpkg format: compress the whole heap

Instead of handling compression for individual file/attribute data we
do now compress the whole heap where they are stored. This
significantly improves compression ratios. We still divide the
uncompressed data into 64 KiB chunks and use a chunk offset array for
the compressed chunks to allow for quick random access without too much
overhead. The tradeoff is a limited possible compression ratio -- i.e.
we won't be as good as tar.gz (though surprisingly with my test
archives we did better than zip).

The other package file sections (package attributes and TOC) are no
longer compressed individually. Their uncompressed data are simply
pushed onto the heap where the usual compression strategy applies. To
simplify things the repository format has been changed in the same
manner although it doesn't otherwise use the heap, since it only stores
meta data.

Due to the data compression having been exposed in public and private
API, this change touches a lot of package kit using code, including
packagefs and the boot loader packagefs support. The latter two haven't
been tested yet. Moreover packagefs needs a new kind of cache so we
avoid re-reading the same heap chunk for two different data items it
contains.

packagefs: Add support for hpkg format V1

* Add union-like class PackageData which wraps the V1 and V2
BPackageData classes.
* GlobalFactory: Create a data reader depending on the data format
version.
* Package: Add a loader for V1 format and try that, if the other one
fails.

package kit: internalize BPackageDataReader

It is no longer public (or even private) API. BPackageDataReaderFactory
returns a BAbstractBufferedDataReader instead. The advantage is that
the latter doesn't have hpkg format specific dependencies.

packagefs: Share string instances globally

Introduce a class String which refers to shared private data that is
registered in a global hash table (in class StringPool) and use the
class consequently. This eliminates duplicate allocations for the same
string and also speeds up tests for equality. There's quite a bit
overhead for the management structures (apparently even more than for
the string data itself), but due to almost all strings being used
multiple times this still almost halves the memory usage for string
data.

packagefs: Organize sources into subdirectories