multimedia/gstreamer1-plugins-rust: convert options into subpackages

[jbeich]

Summary

Allow headless, Gtk3-only or Qt-only users avoid Gtk4 dependency. All plugins without extra dependencies remain in main subpackage, similar to gstreamer1-plugins-{good,bad,ugly} packages..

Note, cairo and pango subpackage names don't match plugin names. Options try to keep global settings (via OPTIONS_{,UN}SET) in mind while subpackages follow option names for consistency.

Test Plan

$ poudriere testport -j 132amd64 multimedia/gstreamer1-plugins-rust~gtk4
[...]
===========================================================================
=>> Checking shared library dependencies
 0x0000000000000001 NEEDED               Shared library: [libc.so.7]
 0x0000000000000001 NEEDED               Shared library: [libgcc_s.so.1]
 0x0000000000000001 NEEDED               Shared library: [libgio-2.0.so.0]
 0x0000000000000001 NEEDED               Shared library: [libglib-2.0.so.0]
 0x0000000000000001 NEEDED               Shared library: [libgobject-2.0.so.0]
 0x0000000000000001 NEEDED               Shared library: [libgraphene-1.0.so.0]
 0x0000000000000001 NEEDED               Shared library: [libgstgl-1.0.so.0]
 0x0000000000000001 NEEDED               Shared library: [libgstreamer-1.0.so.0]
 0x0000000000000001 NEEDED               Shared library: [libgstvideo-1.0.so.0]
 0x0000000000000001 NEEDED               Shared library: [libgtk-4.so.1]
 0x0000000000000001 NEEDED               Shared library: [libm.so.5]
 0x0000000000000001 NEEDED               Shared library: [libthr.so.3]

$ poudriere testport -j 132i386 multimedia/gstreamer1-plugins-rust
[...]
===========================================================================
=>> Checking shared library dependencies
 0x00000001 NEEDED               Shared library: [libc.so.7]
 0x00000001 NEEDED               Shared library: [libcrypto.so.111]
 0x00000001 NEEDED               Shared library: [libgcc_s.so.1]
 0x00000001 NEEDED               Shared library: [libgio-2.0.so.0]
 0x00000001 NEEDED               Shared library: [libglib-2.0.so.0]
 0x00000001 NEEDED               Shared library: [libgobject-2.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstapp-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstaudio-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstbase-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstnet-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstpbutils-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstreamer-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstrtp-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstsdp-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstvideo-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstwebrtc-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libm.so.5]
 0x00000001 NEEDED               Shared library: [libssl.so.111]
 0x00000001 NEEDED               Shared library: [libthr.so.3]

$ poudriere testport -j 132i386 multimedia/gstreamer1-plugins-rust~csound
[...]
===========================================================================
=>> Checking shared library dependencies
 0x00000001 NEEDED               Shared library: [libc.so.7]
 0x00000001 NEEDED               Shared library: [libcsound64.so.6.0]
 0x00000001 NEEDED               Shared library: [libgcc_s.so.1]
 0x00000001 NEEDED               Shared library: [libglib-2.0.so.0]
 0x00000001 NEEDED               Shared library: [libgobject-2.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstaudio-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstbase-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libgstreamer-1.0.so.0]
 0x00000001 NEEDED               Shared library: [libthr.so.3]

[jbeich]

• Move graphene dependency from main to gtk4 subpackage
• Propagate USE_GSTREAMER into subpackages