[mlir][Transforms] Make 1:N function conversion pattern interface-based

This commit turns the 1:N dialect conversion pattern for function
signatures into a pattern for `FunctionOpInterface`. This is similar to
the interface-based pattern that is provided with the 1:1 dialect
conversion (`populateFunctionOpInterfaceTypeConversionPattern`). No
change in functionality apart from supporting all `FunctionOpInterface`
ops and not just `func::FuncOp`.