PackageInstaller: Use newly created BString::IEndsWith()

...to find files with .pdb extension

Code was subtly wrong in 2 cases:
1) File that ended in pdb but not an extension e.g. filepdb
erroneously included
2) File that ended in .PDB or other case erroneously skipped

LegacyPackageInstaller: Fix strnlen/strncmp usage.

I should have my "License to C" revoked...

LegacyPackageInstaller: Ignore files which do not end in ".pdb".

The LegacyPackageInstaller's data folder is (and has always been)
"~/config/packages", which is of course the same directory that Haiku's
(relatively) new package management system uses. We don't want the
"administrative" folder and any HPKGs in that directory to show up in
the "installed legacy packages" list, so ignore them.

LegacyPackageInstaller: Fix x86_64 build.

Revert "PackageInstaller: Attempt to fix 64-bit build."

This reverts commit bb4cd92eae8ab7bf2b39110899cf8de33c592b98.

We probably should change this API before R2.

PackageInstaller: Attempt to fix 64-bit build.

PackageInstaller: Fix layout in UninstallView, use BLayoutBuilder.

PackageInstaller: Merge "InstalledPackages" and "PackageInstaller".

Now if you start LegacyPackageInstaller with no filenames passed, you get
the "installed packages" window, from which you can uninstall stuff.

Fixes #10612.