[AArch64] Reland "Improve TargetParser API"

Reworked after several other major changes to the TargetParser since
this was reverted. Combined with several other changes.

Inline calls for the followi

[AArch64] Reland "Improve TargetParser API"

Reworked after several other major changes to the TargetParser since
this was reverted. Combined with several other changes.

Inline calls for the following macros and delete AArch64TargetParser.def:
AARCH64_ARCH, AARCH64_CPU_NAME, AARCH64_CPU_ALIAS, AARCH64_ARCH_EXT_NAME

Squashed changes from D139278 and D139102.

Differential Revision: https://reviews.llvm.org/D138792

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[Support] Move TargetParsers to new component

This is a fairly large changeset, but it can be broken into a few
pieces:
- `llvm/Support/*TargetParser*` are all moved from the LLVM Support
componen

[Support] Move TargetParsers to new component

This is a fairly large changeset, but it can be broken into a few
pieces:
- `llvm/Support/*TargetParser*` are all moved from the LLVM Support
component into a new LLVM Component called "TargetParser". This
potentially enables using tablegen to maintain this information, as
is shown in https://reviews.llvm.org/D137517. This cannot currently
be done, as llvm-tblgen relies on LLVM's Support component.
- This also moves two files from Support which use and depend on
information in the TargetParser:
- `llvm/Support/Host.{h,cpp}` which contains functions for inspecting
the current Host machine for info about it, primarily to support
getting the host triple, but also for `-mcpu=native` support in e.g.
Clang. This is fairly tightly intertwined with the information in
`X86TargetParser.h`, so keeping them in the same component makes
sense.
- `llvm/ADT/Triple.h` and `llvm/Support/Triple.cpp`, which contains
the target triple parser and representation. This is very intertwined
with the Arm target parser, because the arm architecture version
appears in canonical triples on arm platforms.
- I moved the relevant unittests to their own directory.

And so, we end up with a single component that has all the information
about the following, which to me seems like a unified component:
- Triples that LLVM Knows about
- Architecture names and CPUs that LLVM knows about
- CPU detection logic for LLVM

Given this, I have also moved `RISCVISAInfo.h` into this component, as
it seems to me to be part of that same set of functionality.

If you get link errors in your components after this patch, you likely
need to add TargetParser into LLVM_LINK_COMPONENTS in CMake.

Differential Revision: https://reviews.llvm.org/D137838

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