Add a bit to TargetInfo to specify that vectors are element-aligned
rather than naturally aligned. This is needed to match DirectX's Data
Layout in LLVM.
Note that this removes the `Opts.HLSL` early exit from
`checkDataLayoutConsistency` so that we actually get these checks when
compiling HLSL. This check looks like it was put there because of
similarity between OpenCL and HLSL, but it isn't actually necessary.
Resolves#123968
Adds support for elementwise and aggregate splat casting struct types
with bitfields. Replacing existing Flattening function which used to
produce a list of GEPs representing a flattened object with one that
produces a list of LValues representing a flattened object. The LValues
can be used by EmitStoreThroughLValue and EmitLoadOfLValue, ensuring
bitfields are properly loaded and stored. This also simplifies the code
in the elementwise and aggregate splat casting functions.
Closes#125986
Implement HLSLElementwiseCast excluding support for splat cases
Do not support casting types that contain bitfields.
Partly closes#100609 and partly closes#100619
