[MLIR] Add a second map for registered OperationName in MLIRContext (NFC) (#87170)

This speeds up registered op creation by 10-11% by allowing lookup by
TypeID instead of StringRef.

This can break your build/tests at runtime with an error that you're creating
an unregistered operation that you have registered. If so you are likely using
a class inheriting from the "real" operation. See for example in this patch the
case of:

  class ConstantIndexOp : public arith::ConstantOp {


If one is using `builder.create<ConstantIndexOp>()` they actually create an
`arith.constant` operation, but the builder will fetch the TypeID for 
the `ConstantIndexOp` class which does not correspond to any registered
operation. To fix it the `ConstantIndexOp` class got this addition:

  static ::mlir::TypeID resolveTypeID() { return TypeID::get<ConstantOp>(); }