Implement texture functions for Metal target (#4158)

* Impl texture APIs for Metal target

This commit is to implement texture functions for Metal target.

The following functions are implemented and tested.
 - GetDimensions()
 - CalculateLevelOfDetail()
 - CalculateLevelOfDetailUnclamped()
 - Sample()
 - SampleBias()
 - SampleLevel()
 - SampleCmp()
 - SampleCmpLevelZero()
 - Gather()
 - SampleGrad()
 - Load()

Metal has limited support for the texture functions compared to HLSL.
 - LOD is not supported for 1D texture,
 - Depth textures are limited to 2D, 2DArray, Cube and CubeArray
   textures.
 - "Offset" variants are limited to 2D, 2DArray, 2D-Depth,
   2DArray-Depth and 3D textures.

The functions that cannot be implemented for Metal should properly
be handled by the capability system later.

* Fix the failing test, multi-file.hlsl

I am not sure why this change is needed.

* Fix compile errors on macOS 2nd try

* Remove a typo character to fix the compile error

* Trivial clean up

* Remove `as_type` where it was intended as static_cast

* Use a simpler sytax for __intrinsic_asm

* Trivial clean up

* Remove TEST_AFTER_FIXING_CAPABILITY_PROBLEM after fixing normalize

* Fix the failing test properly

* Fix an incorrect setup of Depth-cube texture

---------

Co-authored-by: Yong He <yonghe@outlook.com>

0 files changed, 0 insertions, 0 deletions