Add check already fixed variables in PostponedArgumentInputTypesResolver during adding constraints on them and using inside a functional type

^KT-42374 Fixed

compiler/testData/diagnostics/tests/inference/completion/postponedArgumentsAnalysis/fixingVariableDuringAddingConstraintForFirstPosponedArgument.kt

@@ -0,0 +1,8 @@
+// FIR_IDENTICAL
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_ANONYMOUS_PARAMETER
+
+fun f(p: (Int) -> (String) -> Unit) {}
+
+fun g(cond: Boolean) {
+    f(if (cond) { i -> { } } else { i -> { } })
+}

compiler/testData/diagnostics/tests/inference/completion/postponedArgumentsAnalysis/fixingVariableDuringAddingConstraintForFirstPosponedArgument.txt

@@ -0,0 +1,4 @@
+package
+
+public fun f(/*0*/ p: (kotlin.Int) -> (kotlin.String) -> kotlin.Unit): kotlin.Unit
+public fun g(/*0*/ cond: kotlin.Boolean): kotlin.Unit