[TableGen][InstrInfo] Cull mapping that have not been enabled/not needed (#126137)

- Detect whether logical operand mapping/named operand mappings have 
  been enabled in a previous pass over instructions and execute the
  relevant emission code only if those mappings are enabled.
- For these mappings, skip the fixed set of predefined instructions as
  they won't have these mappings enabled.
- Emit operand type mappings only for X86 target, as they are only used
  by X86 and look for X86 specific `X86MemOperand`.
- Cleanup `emitOperandTypeMappings` code: remove code to handle empty
  instruction list and use range for loops.

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