feat: VA-API support for linux.

[cloudwebrtc]

vaapi works now, but there are some things need to confirm.

• can call drm driver for h264 encoding for AMD/APU
• check rate control is effective
• confirm encoder adapts to resolution changes
• check support for Intel CPU
• check and confirm for H.264 encoding in baseline, main & high profiles
• simulcast support (maybe in next commit)
• add capability detection support for vaapi encoder factory

[cloudwebrtc]

Tried to install libva win32 today run it on windows (via vaon12 driver based on d3d12), but unfortunately it didn't work, the encoder can be opened but the bitstream cannot be encoded. so at this moment we can only support linux

[cloudwebrtc]

required dependencies for AMD GPU.

sudo apt install -y libva-dev libdrm-dev mesa-va-drivers

Confirm that vainfo contains VAProfileH264 and VAEntrypointEncSlice

$ vainfo
Trying display: wayland
libva info: VA-API version 1.22.0
libva info: Trying to open /usr/lib/x86_64-linux-gnu/dri/radeonsi_drv_video.so
libva info: Found init function __vaDriverInit_1_22
libva info: va_openDriver() returns 0
vainfo: VA-API version: 1.22 (libva 2.22.0)
vainfo: Driver version: Mesa Gallium driver 25.0.3-1ubuntu2 for AMD Radeon Graphics (radeonsi, gfx1150, LLVM 19.1.7, DRM 3.63, 6.15.1-061501-generic)
vainfo: Supported profile and entrypoints
VAProfileH264ConstrainedBaseline:	VAEntrypointVLD
      VAProfileH264ConstrainedBaseline:	VAEntrypointEncSlice
      VAProfileH264Main               :	VAEntrypointVLD
      VAProfileH264Main               :	VAEntrypointEncSlice
      VAProfileH264High               :	VAEntrypointVLD
      VAProfileH264High               :	VAEntrypointEncSlice