x264 support in .aar target

[abe-winter]

Do not merge

• wait for factor out graphviz dependency from web_c viamrobotics/rdk#3777 in upstream
• need to retest streaming on build fd99e89 (below)

Working artifact

• https://github.com/viamrobotics/rdk-apk/actions/runs/8590421018 based on fd99e89
• this has libx264.so with soname fix

What changed

• android builds previously had no StreamConfig. Now they have one with just video (no audio)
• moved android-related make commands to new android.make
• add separate droid-rdk.*.aar outputs for amd64 and arm64. needed this for the linker to work, but could be useful to release single-platform APKs at some point (they're 100mb instead of 200mb)
• build-x264.sh for creating arm + x86 libx264.so
• robot/web changes -- graphviz factored out of web_c.go, other flagging changes. when we merge to upstream, I will probably apply this as a separate change to make review easier.

Why

Streaming support

Cleanup + notes

• the no_cgo flag changes should be merged soonish to upstream -- copying functions like this gets stale quickly
• commented vars in android.make + build-x264.sh -- may need some of this to build on mac
• no_cgo now has a lot of cgo. that's okay (android is the only user for now)
• entrypoint_*.go has too many variants, we can significantly reduce I suspect -> remove windows, merge linux + unix
• remove server-android + NDK_ROOT from android.make once RDK CI can build the AAR (don't need the full APK to run on every build though)

[abe-winter]

converted to draft while I merge droid-apk into this

[seanavery]

• Tested that x264 encoder factory setup is working on Android.
• Livestream pipeline from rdk to app successful.