[AArch64] Refactor and move common code to AArch64PrologueEpilogue (NFCI) (#158920)

This is the final patch in a series reworking the structure of the
prologue/epilogue code. This patch moves some methods from
`AArch64FrameLowering` to `Arch64PrologueEpilogue` as they are only used
by `.emitPrologue/Epilogue`. This includes:

- `shouldCombineCSRLocalStackBump()`
- `shouldCombineCSRLocalStackBumpInEpilogue()`
- `allocateStackSpace()`
- `convertCalleeSaveRestoreToSPPrePostIncDec()`
- `fixupCalleeSaveRestoreStackOffset()`

Common code/methods have been factored into a
`AArch64PrologueEpilogueCommon` base class used by both
`AArch64PrologueEmitter` and `AArch64EpilogueEmitter`.

Finally, some redundant fetching of target classes has been removed from
methods.

Author: MacDue