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/invokeOverload2.kt

@@ -1,8 +1,8 @@
 fun foo() {
-    val x = fun(s: String) {}
+    val <!UNUSED_VARIABLE!>x<!> = fun(s: String) {}
 
     fun nested() {
-        val <!UNUSED_VARIABLE!>x<!> = fun(i: Int) {}
+        val x = fun(i: Int) {}
 
         x(10)
     }