Introduce Unit-conversions for simple arguments

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

@@ -0,0 +1,18 @@
+// !LANGUAGE: +UnitConversion +SuspendConversion
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION
+
+fun interface SuspendRunnable {
+    suspend fun run()
+}
+
+fun foo(r: SuspendRunnable) {}
+
+fun bar(): String = ""
+
+abstract class SubInt : () -> Int
+
+fun test(f: () -> String, s: SubInt) {
+    foo(f)
+    foo(s)
+    foo(::bar)
+}