GODEBUG can affect how we type-check code, due to the gotypesalias
setting.

Generic functions can instantiate generic types with type parameters,
which can lead to methods with duplicated names. We handle this by using
a generic-specific synthetic constant. However, we also generate
wrappers for these instantiated methods, which leads to more duplicated
names, and the code doesn't easily let us figure out that the wrapper is
for an instantiated method. Instead of working around this further,
remove the test for unique function names. Function names weren't unique
in practice, anyway, because of test variants of packages.

We've never cared about these statistics when running the test. Now it
is much simpler to tell what the test is actually testing: that building
the IR form of all packages in stdlib doesn't panic.

Go 1.22 introduced go/types.Alias, a node that explicitly encodes type
aliases. GODEBUG=gotypesalias=1 enables this behavior. In Go 1.23, that
setting will become the new default.

Update all code that compares types (via equality, string equality, or
type assertions) to account for aliases. Most checks don't require
changes, as they operate on underlying types. For the remainder, a mix
of types.Unalias and explicit handling of aliases is necessary.

Closes: gh-1523