[clang] [Clang] Treat `ext_vector_type` as a regular type attribute (PR #130177)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> I think vector types as a type attribute are reasonable, at least at first blush. However, if we're talking about redesigning the feature to expose it in a more natural way, we should consider what proposals are in front of the C and C++ standards committees.

This mostly just makes these easier to use, they come from https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_C.html#built-in-vector-data-types originally but they map pretty well to the LLVM vectors. I agree it would be nice to have this type of stuff in the standard someday.

https://github.com/llvm/llvm-project/pull/130177