Crash with conflicting fn definitions in CheckFunctionTypeMatches()

[danakj]

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Description of the bug:

interface Ptr {
  let Type:! type;
}
final impl forall [U:! type] U as Ptr where .Type = U* {}

fn F1[T:! Ptr](var t: T) -> T.(Ptr.Type) {
  return &t;
}

fn F1[T:! Ptr](var t: T) -> T.Type {
  return &t;
}

This crashes the toolchain.

-> 212      CARBON_CHECK(Is<TypedInst>(), "Casting inst {0} to wrong kind {1}", *this,
   213                   Info::DebugName());

In merge.cpp:265:34

   263    auto new_name_id =
   264        context.entity_names()
-> 265            .Get(new_param_pattern.As<SemIR::AnyBindingPattern>().entity_name_id)
   266            .name_id;

It does As<AnyBindingPattern> but the pattern is VarPattern, which is not a BindingPattern or SymbolicBindingPattern.

What did you do, or what's a simple way to reproduce the bug?

No response

What did you expect to happen?

No response

What actually happened?

No response

Any other information, logs, or outputs that you want to share?

No response