[ARM][AArch64] autogenerate header file for TargetParser from Target tablegen files (#88378)

Introduce a mechanism to share data between the ARM and AArch64 backends and
TargetParser, to reduce duplication of code. This is similar to the current
RISC-V implementation.

The target tablegen file (in this case `ARM.td` or `AArch64.td`) is
processed during building of `TargetParser` to generate the following
files in the build tree:
 - `build/include/llvm/TargetParser/ARMTargetParserDef.inc`
 - `build/include/llvm/TargetParser/AArch64TargetParserDef.inc`

For now, the use of these generated files is limited to files _outside_
of `TargetParser`. The main reason for this is that the modifications to
`TargetParser` will require additional data added to the tablegen files,
which I want to split into separate PRs.