[BOLT] Improve code sharing between AArch64MCPlusBuilder and core AArch64InstrInfo

[atrosinenko]

The duplication of code to get various properties of the instructions between BOLT's AArch64MCPlusBuilder and AArch64InstrInfo from LLVM core was mentioned several times throughout discussing the patches for gadget scanner:

• the discussion of [BOLT][AArch64] Do not crash on authenticated branch instructions #129898
• this thread [BOLT] Gadget scanner: detect signing oracles #134146 (comment) in [BOLT] Gadget scanner: detect signing oracles #134146
• these threads [BOLT] Gadget scanner: clarify MCPlusBuilder callbacks interface #136147 (comment), [BOLT] Gadget scanner: clarify MCPlusBuilder callbacks interface #136147 (comment) in [BOLT] Gadget scanner: clarify MCPlusBuilder callbacks interface #136147

Creating a dedicated issue on this topic.

[llvmbot]

@llvm/issue-subscribers-bolt

Author: Anatoly Trosinenko (atrosinenko)

The duplication of code to get various properties of the instructions between BOLT's `AArch64MCPlusBuilder` and `AArch64InstrInfo` from LLVM core was mentioned several times throughout discussing the patches for gadget scanner:

• the discussion of #129898
• this thread [BOLT] Gadget scanner: detect signing oracles #134146 (comment) in #134146
• these threads [BOLT] Gadget scanner: clarify MCPlusBuilder callbacks interface #136147 (comment), [BOLT] Gadget scanner: clarify MCPlusBuilder callbacks interface #136147 (comment) in #136147

Creating a dedicated issue on this topic.