KT-64832 KT-61032 [FIR] Correctly handle extension receiver from implicit invoke calls in UnusedChecker

- use `FirImplicitInvokeCall` instance check to detect implicit calls,
it is cleaner than checking particular resolve type and "invoke" name
- reuse `visitQualifiedAccesses` to update the CFG instead of manually
searching through the `localProperties` (because it didn't work in the
case of overloads)

^KT-64832 Fixed
^KT-61032 Fixed

compiler/fir/analysis-tests/testData/resolve/extendedCheckers/unused/invokeKFunction.kt

@@ -2,7 +2,7 @@
 import kotlin.reflect.KFunction1
 
 fun foo(action: KFunction1<String, Int>): Int {
-    val <!UNUSED_VARIABLE!>localAction<!> = action
+    val localAction = action
 
     return localAction("hello")
 }