FIR: rewrite lambda return type inference

* `return` should only be added to the last statement if the return
   type is not Unit

 * If there is a `return` without an argument, then the expected return
   type is Unit and the last expression is not a return argument (unless
   it's an incomplete call, in which case it is inferred to return Unit;
   this behavior is questionable, but inherited from K1)

 * There should be a constraint on return arguments even if the expected
   type is Unit, otherwise errors will be missed

 * When the expected type is known, using the call completion results
   writer is pointless (and probably subtly wrong).

^KT-54742 Fixed

compiler/testData/diagnostics/tests/regressions/resolveCollectionLiteralInsideLambda.fir.kt

@@ -3,5 +3,5 @@
 fun foo(l: () -> Unit) {}
 fun bar(l: () -> String) {}
 
-val a = foo { <!UNSUPPORTED!>[]<!> }
-val b = bar { <!UNSUPPORTED!>[]<!> }
+val a = foo { <!ARGUMENT_TYPE_MISMATCH, UNSUPPORTED!>[]<!> }
+val b = bar { <!ARGUMENT_TYPE_MISMATCH, UNSUPPORTED!>[]<!> }