Handle old given syntax where identifier and type are seperated by new line (scala#21957)

Fixes scala#21768

Fixes usages of `with {...}` and `= new {}` declarations presented in
tests.

Author: WojciechMazur

tests/pos/i21768.scala

@@ -0,0 +1,12 @@
+
+trait Foo[T]:
+  def foo(v: T): Unit
+
+given myFooOfInt:
+  Foo[Int] with
+  def foo(v: Int): Unit = ???
+
+given myFooOfLong:
+  Foo[Long] = new Foo[Long] {
+    def foo(v: Long): Unit = ???
+  }