ambiguous call matches both Int8 and Int16

[straight-shoota]

The following code errors:

a = 1 || "foo"
a + 2 # instantiating '(Int32 | String)#+(Int32)':  ambiguous call matches both Int8 and Int16

It's odd that this mentions Int8 and Int16 which are not even used explicitly in this example. I guess it's because when the literal type is expanded it first notices that these could be ambiguous. It should definitely not compile because String#+ doesn't accept any integer, but the error message is wrong.

Even if the integer literals are typed explicitly, the error is similar:

a = 1_i32 || "foo"
a + 2_i32 # instantiating '(Int32 | String)#+(Int32)': ambiguous call matches both Int8 and Int16

The expected error should be something like no overload matches '(Int32 | String)#+' with type Int32.

Extracted from #6593

Introduced by #6074