Prefer user types over built in types

Example:
My program is very special; ints are 5 bytes, and unsigned. I can define that very easily:

mySpecialInt = Type.int(5, False)
bv.define_user_type("int", mySpecialInt)

But when I select an argument, press Y, and type int, it gets replaced with a int32_t.

This makes me sad.

If I do:

old = current_function.function_type
current_function.function_type = types.Type.function(old.return_value, [mySpecialInt], old.calling_convention, old.has_variable_arguments, old.stack_adjustment)

The argument does get overwritten with my custom int class, but in this case displays it as uint40_t, which I think is less than ideal (possibly related to #1666, of which I think I disagree with the outcome of).

Perhaps this should be separated into two issues; one for the type-entry box not understanding int to be my user-defined typedef overriding the built-in int, and another for not displaying the type as what I entered and instead mapping it to the base type.

Edit: The solution to the display problem is to define the type as mySpecialInt = Type.int(5, False, "int"), so this issue is only for the remaining UI bug.

Start with the type-entry flow described in the issue: select an argument, press Y, and enter int after defining a user type named int. Trace where that input resolves to the built-in int32_t, then verify that the user-defined type is preferred and remains visible after the change.