[mlir][tblgen] Generate builders with inferred return types and unwrapped attributes

This diff causes mlir-tblgen to generate code for an additional builder for an
operation argument with a return type that can be inferred *AND* an attribute in
the argument list can be "unwrapped." (Previously, the unwrapped build function
was only generated for builders with explicit return types in separate or
aggregate form.) As an example, this builder might be used by code that creates
operations that implement the `SameOperandsAndResultType` interface. A test case
was created.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D124043