Opt: Opaque Inliner Needed

Create inliner pass which *only* inlines function calls with opaque arguments or return value.

This pass is part of an effort to assist glslang in creating valid SPIR-V from HLSL shaders which store and load opaque objects.

The algorithm will start by performing the inlining only in entry point functions. After the inlining for a function is complete, the functions of the remaining function calls are added to the list to be processed.

Claimed by @greg-lunarg and started.

Start from the entry point functions described in the issue and determine how calls with opaque arguments or return values should be selected before processing remaining callees. Done means the pass handles the stated inlining sequence and assists glslang in producing valid SPIR-V for HLSL shaders; the work is already claimed and started.

Written by the indexing model from the issue text.