Don't perform Unit-conversion for functional types with type variables

#KT-40269 Fixed

compiler/testData/diagnostics/tests/unitConversion/noUnitConversionForGenericTypeFromArrow.kt

@@ -0,0 +1,12 @@
+// FIR_IDENTICAL
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+class Either
+
+infix fun <A, B, C> ((A) -> B).andThen(g: (B) -> C): (A) -> C = TODO()
+
+fun unsafeRunAsync(cb: (Either) -> Unit) {}
+
+fun runAsync(cb: (Either) -> Unit) {
+    unsafeRunAsync(cb.andThen { })
+}

compiler/testData/diagnostics/tests/unitConversion/noUnitConversionForGenericTypeFromArrow.txt

@@ -0,0 +1,12 @@
+package
+
+public fun runAsync(/*0*/ cb: (Either) -> kotlin.Unit): kotlin.Unit
+public fun unsafeRunAsync(/*0*/ cb: (Either) -> kotlin.Unit): kotlin.Unit
+public infix fun </*0*/ A, /*1*/ B, /*2*/ C> ((A) -> B).andThen(/*0*/ g: (B) -> C): (A) -> C
+
+public final class Either {
+    public constructor Either()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/unitConversion/noUnitConversionOnReturningGenericFunctionalType.kt

@@ -0,0 +1,10 @@
+// FIR_IDENTICAL
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+fun <T> foo(f: () -> T) {}
+fun bar(g: () -> Unit) {}
+fun <K> baz(): () -> K = TODO()
+
+fun test() {
+    foo { bar(baz()) }
+}

compiler/testData/diagnostics/tests/unitConversion/noUnitConversionOnReturningGenericFunctionalType.txt

@@ -0,0 +1,6 @@
+package
+
+public fun bar(/*0*/ g: () -> kotlin.Unit): kotlin.Unit
+public fun </*0*/ K> baz(): () -> K
+public fun </*0*/ T> foo(/*0*/ f: () -> T): kotlin.Unit
+public fun test(): kotlin.Unit