[0037] Describe `FeedbackTexture` types and `WriteSamplerFeedback` methods

[inbelic]

The Texture and Sampler Types currently does not provides a description for feedback texture types or their methods.

The proposal must be updated to describe:

• FeedbackTexture2D and FeedbackTexture2DArray types
• WriteSamplerFeedback method
• WriteSamplerFeedbackBias method
• WriteSamplerFeedbackLevel method
• WriteSamplerFeedbackGrad method

AC:

• Proposal updated with FeedbackTexture2D and FeedbackTexture2DArray
  type definitions
• Proposal updated with all WriteSamplerFeedback* method descriptions including their builtin interface, supported types, codegen, and DXIL/SPIR-V lowering
• Create issues for the new work described