feat: list the hardware codecs of the hardware video codec factories

[devopvoid]

Summary

Lets applications tell which video codecs the GPU handles, and makes the hardware codec factories cheaper and more consistent to use.

• getHardwareCodecs() on HardwareVideoEncoderFactory and HardwareVideoDecoderFactory: the supported codecs, in their order, that a hardware encoder or decoder of the machine takes first (on macOS, H.264 through VideoToolbox included). Natively, the composite hardware factories implement WebRTC's QueryCodecSupport and report a format as power efficient when a hardware sub-factory supports it.
• CodecListExample builds its PeerConnectionFactory with the hardware factories and marks every video codec as HARDWARE or SOFTWARE.
• H.264 High 4:4:4 stays off the GPU decoders. NVDEC and Media Foundation offered every H.264 format WebRTC decodes, though GPU decoders take 4:2:0 only, so a 4:4:4 stream failed on the GPU and lost frames until the next key frame reached the software decoder. Both now offer the 4:2:0 profiles only.
• The GPU is probed once per process. The platform's hardware factories are made once per setting of the hardware codec options (webrtc.hardware.vp9Encoder, webrtc.hardware.vaapiExperimental) and shared. A PeerConnectionFactory built with the hardware factories makes them natively, as it does the default ones, instead of going through Java for every codec; before, it probed twice, and the two probes could disagree. A Java factory of one's own makes the built-in factories only when it first hands out a native codec.

On a Windows machine with an AMD GPU, after the first probe of the process, creating both hardware factories takes about 4 ms and the PeerConnectionFactory about 1.3 ms; before, each setup probed twice, about 40 ms per decoder probe.

One behaviour change: a GPU, driver or codec extension installed or removed while the process runs is seen by a new process only. The Javadoc and the video codecs guide say so.

Testing

• mvn -pl webrtc-jni,webrtc package on Windows x64 (AMD GPU): 289 tests, 0 failures, 3 skipped (two macOS-only, the opt-in VP9 encoder).
• New tests: hardware codecs are supported codecs in the same order and include every codec without a software implementation; no H.264 High 4:4:4 among the hardware decoders; a factory built with the hardware factories offers exactly their codecs; a Java factory delegating to HardwareVideoEncoderFactory still encodes H.264 on the GPU; the H.264 and AV1 hardware tests check that the encoded codec is listed as hardware.
• Ran CodecListExample: H.264 Constrained Baseline/Baseline (packetization mode 1), AV1 and H.265 encode in hardware; VP9 profile 0, H.264 4:2:0, AV1 profile 0 and H.265 decode in hardware.
• Not run locally: the NVDEC change (Linux) and the macOS H.264 marking, which CI builds.