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/invokeSuspend.kt

@@ -1,5 +1,5 @@
 suspend fun foo(action: suspend () -> Unit) {
-    val <!UNUSED_VARIABLE!>x<!> = action
+    val x = action
 
     x()
 }