Add CIR lowering support for the non-overloaded NEON intrinsics
`vnegd_s64` and `vnegh_f16`.
The associated tests are shared with the existing default codegen tests:
* `neon-intrinsics.c` → `neon/intrinsics.c`
* `v8.2a-fp16-intrinsics.c` → `neon/fullfp16.c`
A new test file,
* `clang/test/CodeGen/AArch64/neon/fullfp16.c`
is introduced and is intended to eventually replace:
* `clang/test/CodeGen/AArch64/v8.2a-fp16-intrinsics.c`
Since both intrinsics are non-overloaded, the CIR and default codegen
handling is moved to the appropriate switch statements. The previous
placement was incorrect.
This change also includes minor refactoring in `CIRGenBuilder.h` to
better group related hooks.