RDI-3231 Add RDP 4:4:4 GStreamer Elements for AVC444v2 Encoding/Decoding

[msabiniok]

Implements two complementary GStreamer elements (rdp444split and rdp444combine) that handle Microsoft RDP AVC444v2 encoding scheme for splitting and combining 4:4:4 chroma video streams. This allows efficient transmission of full chroma video over two separate 4:2:0 video streams.

rdp444split

• Splits Y444 (4:4:4) input into two I420 (4:2:0) output streams
• Main output: Full luma + even-pixel chroma samples
• Auxiliary output: Odd-pixel chroma samples packed into I420 format
• Implements Microsoft RDP AVC444v2 encoding specification (B1-B9)

rdp444combine

• Combines two I420 (4:2:0) input streams into Y444 (4:4:4) output
• Performs inverse operation of rdp444split
• Reconstructs full chroma resolution from split streams
• Based on GstAggregator for proper stream synchronisation