[FIR] Don't set lambda parameter type to Nothing by default

... when the expected type is not a function type.
Instead set it to a new type variable.
This fixes a bunch of false negative CANNOT_INFER_PARAMETER_TYPE.

#KT-59882 Fixed

compiler/testData/diagnostics/tests/inference/reportingImprovements/FunctionPlaceholder.fir.kt

@@ -7,7 +7,7 @@ fun <T, R> bar(f: (T) -> R) = f
 
 fun test() {
     foo <!ARGUMENT_TYPE_MISMATCH!>{ <!UNRESOLVED_REFERENCE!>it<!> }<!>
-    foo <!ARGUMENT_TYPE_MISMATCH!>{ x -> x}<!>
+    foo <!ARGUMENT_TYPE_MISMATCH!>{ <!CANNOT_INFER_PARAMETER_TYPE!>x<!> -> x}<!>
     foo <!ARGUMENT_TYPE_MISMATCH!>{ x: Int -> x}<!>
 
     <!NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER, NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>bar<!> <!CANNOT_INFER_PARAMETER_TYPE!>{ it + 1 }<!>