[Painless] Add boxed type to boxed type casts for method/return (#36571)

This adds implicit boxed type to boxed types casts for non-def types to create asymmetric casting relative to the def type when calling methods or returning values. This means that a user calling a method taking an Integer can call it with a Byte, Short, etc. legally which matches the way def works. This creates consistency in the casting model that did not previously exist.

Author: jdconrad