[ARM64EC] Warn on using disallowed registers in assembly src. (#93618)

ARM64EC designates a set of disallowed registers, because a mapping does
not exist from them to x64. The MSVC assembler (armasm64) has a warning
for this.

A test is also included as part of the patch.

See the list of disallowed registers below:

https://learn.microsoft.com/en-us/cpp/build/arm64ec-windows-abi-conventions?view=msvc-170#register-mapping