Try to fix callee type inference in typedFunctionValue

[noti0na1]

The callee part is separated from #24697 for further investigation

When typing a function literal's expression to infer the callee type, we now create placeholder tree for each argument, and make sure the function part does not refer to any parameter. This ensures that references in the expression won't incorrectly resolve to outer scope variables with the same names as the parameters.

Fix the following test:

def foo[T <: (B => Unit)](f: T) = ???
def transfer(in: A): Unit =
  foo(in => transfer(in)) // error: Found: (in : B) Required: A
def transfer(in: B): Unit = ???

[noti0na1]

The last commit contains the stricter rule we discussed yesterday, but it breaks type inference in several tests. @odersky