[AArch64][llvm] Generate asm parser extension map from TableGen (NFC)
Modify ARMTargetDefEmitter to emit the assembly parser `ExtensionMap[]`
and replace the hand-written table in AArch64AsmParser.cpp with the
generated one.
Keep the assembly parser-only quirks in the emitter: the directive
denylist, the legacy primary spellings for `mte` and `compnum`, and the
extra bits needed for the `sve2-*` shorthand extensions.
This removes the duplicate manual table while preserving existing
directive parsing and required-feature diagnostics.