Find Usages: Support text-file search of Kotlin declarations

idea/testData/findUsages/kotlin/findClassUsages/classUsedInPlainText.0.kt

@@ -0,0 +1,7 @@
+// PSI_ELEMENT: org.jetbrains.jet.lang.psi.JetClass
+// OPTIONS: textOccurrences
+package test
+
+class <caret>Foo {
+
+}

idea/testData/findUsages/kotlin/findClassUsages/classUsedInPlainText.1.text

@@ -0,0 +1,2 @@
+test.Foo
+Foo

idea/testData/findUsages/kotlin/findClassUsages/classUsedInPlainText.results.txt

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+Unclassified usage (1: 1) test.Foo

idea/testData/findUsages/kotlin/findFunctionUsages/functionUsedInPlainText.0.kt

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+// PSI_ELEMENT: org.jetbrains.jet.lang.psi.JetNamedFunction
+// OPTIONS: textOccurrences
+package test
+
+class Foo {
+    fun <caret>foo() {
+
+    }
+}

idea/testData/findUsages/kotlin/findFunctionUsages/functionUsedInPlainText.1.text

@@ -0,0 +1 @@
+Function foo is defined in class Foo

idea/testData/findUsages/kotlin/findFunctionUsages/functionUsedInPlainText.results.txt

@@ -0,0 +1 @@
+Unclassified usage (1: 10) Function foo is defined in class Foo