[core-kit] Profile updates are needed after many changes in testing branches

This Issue is intended to track the profile updates that are needed to prevent `USE` flag--related errors when emerging packages in our tree.

At least these are needed:
```
dev-libs/libxml2 lzma

# qemu needs this one
dev-libs/libpcre2 static-libs

app-crypt/gcr gtk
media-libs/gst-plugins-ugly a52dec mpeg2dec
net-fs/samba ads acl

# USE=postproc flag breaks emerge for me
media-video/transcode -postproc
```

And for `@kde-plasma` we need these:
```
virtual/kde-seed gui wayland libproxy sql
virtual/kde-seed multimedia libinput
```

Review the testing-branch profiles for the listed package and USE flag combinations, starting with the entries for libxml2, libpcre2, qemu, KDE Plasma, and the other packages shown. Verify the profile updates by emerging the affected packages and confirm that the reported USE-related errors no longer occur.

Written by the indexing model from the issue text.