Introduce Unit-conversions for simple arguments

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

@@ -0,0 +1,15 @@
+// !LANGUAGE: +UnitConversion
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION
+
+fun interface KRunnable {
+    fun run()
+}
+
+fun foo(r: KRunnable) {}
+
+abstract class SubInt : () -> Int
+
+fun test(f: () -> Int, s: SubInt) {
+    foo(f)
+    foo(s)
+}