[FIR] Prevent missing diagnostics on free lambdas

The change in `FirPsiDiagnosticTestGenerated.Resolve#testCast`
only highlights the existing
problem that we don't assign a
valid type to `_`.

^KT-58906 Fixed

compiler/testData/diagnostics/tests/inference/invokeLambdaAsFunction.fir.kt

@@ -1,7 +1,7 @@
-fun test1(i: Int) = { i ->
+fun test1(i: Int) = { <!VALUE_PARAMETER_WITH_NO_TYPE_ANNOTATION!>i<!> ->
     i
 }(i)
 
-fun test2() = { i -> i }<!NO_VALUE_FOR_PARAMETER!>()<!>
+fun test2() = { <!VALUE_PARAMETER_WITH_NO_TYPE_ANNOTATION!>i<!> -> i }<!NO_VALUE_FOR_PARAMETER!>()<!>
 
-fun test3() = { i -> i }(1)
+fun test3() = { <!VALUE_PARAMETER_WITH_NO_TYPE_ANNOTATION!>i<!> -> i }(1)

compiler/testData/diagnostics/tests/inference/kt12399.fir.kt

@@ -1,3 +1,3 @@
 fun foo(a: Any) {
-    foo({ index -> } {  })
+    foo({ <!VALUE_PARAMETER_WITH_NO_TYPE_ANNOTATION!>index<!> -> } {  })
 }

compiler/testData/diagnostics/tests/inference/nonFunctionalExpectedTypeForLambdaArgument.fir.kt

@@ -32,5 +32,5 @@ fun testParamCall() {
 }
 
 fun testNoContext() {
-    { it -> it }
+    { <!VALUE_PARAMETER_WITH_NO_TYPE_ANNOTATION!>it<!> -> it }
 }