Fix MatchError in wildcardArgOK for mixed wildcard/concrete type args

[tanishiking]

Fix #25000

The wildcardArgOK function in overload resolution would crash with a MatchError when the argument type had mixed wildcard and concrete type arguments on an invariant type (e.g., java.util.Map[String, ? <: V]).

The partial function only handled TypeBounds but String is a TypeRef, causing the pattern match to fail. Added a general case that returns true if two types are same for non-wildcard arguments.

Maybe we should return true here and defer their validation to the main isCompatible check?

[tanishiking]

We still have an overload checking regression when both formal and argtpe are TypeBounds

trait Format
trait Codec[L, H, F <: Format]  // invariant

trait Variant[O] {
  def codec: Codec[?, O, ? <: Format]
}

class Test {
  def decode[L, H](codec: Codec[L, H, ? <: Format]): H = ???
  def decode[L, H](other: String): H = ???

  def test[O](v: Variant[O]): O = decode(v.codec)
  // None of the overloaded alternatives of method decode in class Test with types
  //  [L, H](other: String): H
  //  [L, H](codec: Codec[L, H, ? <: Format]): H
  // match arguments ((v.codec² : => Codec[?, O, ? <: Format]))
  // 
  // where:    codec  is a reference to a value parameter
  //           codec² is a method in trait Variant
  //
  // v.codec: Codec[?, O, ? <: Format]
  // formal:  Codec[L, H, ? <: Format]
  // Pairs: (?, L), (O, H), (? <: Format, ? <: Format)
  //
}