[HLSL] vector size and type errors have no source location

[pow2clk]

Vectors with invalid sizes or types will display no code location for their errors given that they are defined in HLSLExternalSemaSource and not a line of HLSL. The accompanying notes will show the proper lines of code, but the errors having no location make it impossible to write verify tests for these errors

See https://godbolt.org/z/7jT7Trh8K

Proposed solution: use concepts to verify the vector size, this will generate error messages pointing at the correct line. Assumption for estimates here is that we've worked through all the issues around making this work well as part of our resource element type validation solution.