[AArch64][clang] Use tablegen rather than hard-coded feature dependencies
Refactor AArch64 frontend feature handling so extension relationships come
from the TargetParser extension graph instead of hand-written dependency
code in C++. This makes `llvm::AArch64::ExtensionSet` the source of
truth for dependency expansion while still keeping the short `Has...` names
used in the frontend code.
This removes a large amount of duplicated implication logic from
`handleTargetFeatures` and related feature queries. The frontend now
rebuilds its extension state from TableGen-derived data and then derives
its cached feature state from that, rather than maintaining parallel
dependency rules in C++.
I also preserved several pieces of historical frontend behaviour that are
not represented directly in the extension graph. Explicit disables such as
`no-sme` still win after implied-feature expansion, direct `+fullfp16` and
`+jscvt` still restore the expected NEON-facing state, and SME-family
features no longer incorrectly appear to enable AdvSIMD/NEON.
Finally, I added regression coverage for the direct-feature and explicit
disable cases uncovered during review, including raw `-target-feature`
combinations and target-attribute cases such as `no-sme`.
llvm-project
95a79df6 - [AArch64][clang] Use tablegen rather than hard-coded feature dependencies
