[NFC][InstrInfoEmitter] Include location of inst definition in comment (#156927)
Print the source location of the instruction definition in comment next
to the enum value for each instruction. To make this more readable,
change formatting of the instruction enums to be better aligned.
Example output:
```
VLD4qWB_register_Asm_8 = 573, // (ARMInstrNEON.td:8849)
VMOVD0 = 574, // (ARMInstrNEON.td:6337)
VMOVDcc = 575, // (ARMInstrVFP.td:2466)
VMOVHcc = 576, // (ARMInstrVFP.td:2474)
VMOVQ0 = 577, // (ARMInstrNEON.td:6341)
```