Migrate `IIT_Info` into `Intrinsics.td`

  - Define `IIT_Info` in `Intrinsics.td`
  - Implement `EmitIITInfo` in `IntrinsicEmitter.cpp`
  - Use generated `IIT_Info` in `Function.cpp`

Depends on D145873 and D146179

Differential Revision: https://reviews.llvm.org/D146914