Add FSR (FidelityFX Super Resolution) shaders for upscaling and sharpening

[Benjamin-Wegener]

Implements AMD FidelityFX Super Resolution with two shader components:

• fsr_easu.fsh: Edge Adaptive Spatial Upsampling for high-quality upscaling
• fsr_rcas.fsh: Robust Contrast Adaptive Sharpening for image enhancement

Features:

• EASU: Edge-aware anisotropic upscaling using Catmull-Rom interpolation
• RCAS: Contrast adaptive sharpening with configurable strength (0.0-1.0)
• Anti-ringing clamp to prevent overshooting artifacts
• Optimized for OpenGL ES with precision handling
• Follows vanilla FSR implementation closely

The FSR-EASU shader provides superior upscaling quality compared to traditional
methods by analyzing local gradients and applying directional filtering along
edges. FSR-RCAS complements this with perceptually-aware sharpening that
preserves color information while enhancing detail.

Both shaders include comprehensive comments explaining the algorithms and
maintain compatibility with the existing PPSSPP shader pipeline.

Closes #17231, #17580, #14689, #14630

[Benjamin-Wegener]

had typo in one filename

[hrydgard]

That is super cool, nice job!

I will have to test it on all three backends a bit before merging, stay tuned.