Introduce UNUSED_ANONYMOUS_PARAMETER for anonymous functions

It is not reported for 1.0 language version because
renaming to _ is not possible. It has weak warning severity

So #KT-8813 Fixed
So #KT-16875 Fixed

compiler/testData/diagnostics/tests/controlFlowAnalysis/unusedInAnonymous.kt

@@ -0,0 +1,9 @@
+// !LANGUAGE: -SingleUnderscoreForParameterName
+// See KT-8813, KT-9631
+
+fun someApi(f: (Int) -> Unit) = f(42)
+
+fun test() {
+    someApi(fun(p: Int) {})
+    // Apparently "p" cannot be removed because the signature is fixed by "someApi
+}