MimeInfoUpdater: Don't touch the MIME DB

Use the new SetIconForType() and SetSupportedTypes() versions and
request the MIME DB not to be updated. This changes the
update_mime_info() and mimeset (without -a/-A) behavior in that they
only modify the (application) file attributes, now. Addresses #10453.

Resolve #10435.

Adjust Database{Location} to only attempt to create a mimetype when
actually necessary, and fail otherwise if a writable version doesn't yet
exist. Correspondingly, adjust callers such as
DatabaseLocation::DeleteAttribute(). Fixes a problem where a caller asking
to perform a mimeset could fail early due to SetSupportedTypes() attempting
to update the read-only mime database entry supplied by a package, and
consequently most of the mimeset operations would be skipped.

MimeInfoUpdater: Fix is_shared_object_mime_type()

The comparison must be case insensitive.

Pull class MimeInfoUpdater out of UpdateMimeInfoThread

* Pull out base class MimeEntryProcessor out of AppMetaMimeCreator.
* Pull class MimeInfoUpdater out of UpdateMimeInfoThread and derive it
from MimeEntryProcessor.
* MimeInfoUpdater: Instead of BMimeType::GuessMimeType(), use
Database::GuessMimeType() directly.

MimeInfoUpdater: Don't touch the MIME DB

Use the new SetIconForType() and SetSupportedTypes() versions and
request the MIME DB not to be updated. This changes the
update_mime_info() and mimeset (without -a/-A) behavior in that they
only modify the (application) file attributes, now. Addresses #10453.

Resolve #10435.

Adjust Database{Location} to only attempt to create a mimetype when
actually necessary, and fail otherwise if a writable version doesn't yet
exist. Correspondingly, adjust callers such as
DatabaseLocation::DeleteAttribute(). Fixes a problem where a caller asking
to perform a mimeset could fail early due to SetSupportedTypes() attempting
to update the read-only mime database entry supplied by a package, and
consequently most of the mimeset operations would be skipped.

MimeInfoUpdater: Fix is_shared_object_mime_type()

The comparison must be case insensitive.

Pull class MimeInfoUpdater out of UpdateMimeInfoThread

* Pull out base class MimeEntryProcessor out of AppMetaMimeCreator.
* Pull class MimeInfoUpdater out of UpdateMimeInfoThread and derive it
from MimeEntryProcessor.
* MimeInfoUpdater: Instead of BMimeType::GuessMimeType(), use
Database::GuessMimeType() directly.