Extract do-patch into a separate script.

[mat]

Summary

Implement EXTRA_PATCH_TREE. (idea from the PR)

[julian]

this is obviously part of a bigger change, so I can't comment on that part but the part about the EXTRA_PATCH_TREE looks like it should work.
I don't see why one would have a compressed patch file but handling it shouldn't hurt. (except by hiding bugs through added complexity.)

[mat]

• Fixup EXTRA_PATCHES missing the :-pX argument.
• Implement EXTRA_PATCH_TREE. (idea from the PR)
• Remove PATCH_WRKSRC from PATCH_ARGS.
• Don't go through apply_one_patch for local files.

[mat]

• Use the framework correctly.
• "Fix" ports using PATCH_ARGS to patch things manually (???)