[0037] Describe the `Store` method and `.sample` operator

[inbelic]

The Texture and Sampler Types does not have a description for the Store method or the .sample[index][pos] operator.

The proposal must be updated to describe:

• The Store method for RWTexture* types, describing the builtin interface, codegen lowering, and DXIL/SPIR-V translation.
• The .sample[index][pos] operator for Texture2DMS and Texture2DMSArray, describing the curried subscript pattern (analogous to .mips[level][pos]).

AC:

• Description of Store method added
• Description of .sample[index][pos] operator added
• Create issues for the new work described