[llvm] [MC][TableGen] Expand Opcode field of MCInstrDesc (PR #179652)

[Jay Foad via llvm-commits]

jayfoad wrote:

Many of the changes in here could have been done as a separate NFC patch that would not have needed reverting. Anything that just updates the type of a local variable of function argument or return value should be pretty safe. (Personally I think there is almost never a good reason for using a type smaller than 32 bits for a variable/argument/return value.)

https://github.com/llvm/llvm-project/pull/179652