Fix search usages for invoke() extension operator (KT-18269)

#KT-18269 Fixed

idea/testData/findUsages/kotlin/conventions/invokeExtension.0.kt

@@ -0,0 +1,11 @@
+// PSI_ELEMENT: org.jetbrains.kotlin.psi.KtNamedFunction
+// OPTIONS: usages
+package pack
+
+class P
+operator fun P.<caret>invoke() = 1
+
+fun f(p: P) {
+    p()
+    p.invoke()
+}

idea/testData/findUsages/kotlin/conventions/invokeExtension.log

@@ -0,0 +1,6 @@
+Resolved p()
+Searched references to pack.P
+Searched references to parameter p of pack.f(p: P) in non-Java files
+Used plain search of pack.invoke() in LocalSearchScope:
+    CLASS:P
+    FUN:invoke

idea/testData/findUsages/kotlin/conventions/invokeExtension.results.txt

@@ -0,0 +1,2 @@
+Function call 10 p.invoke()
+Implicit 'invoke' 9 p()