[FIR IDE] Add find usages tests for FIR plugin

idea/idea-test-framework/test/org/jetbrains/kotlin/idea/test/KotlinLightCodeInsightFixtureTestCase.kt

@@ -24,6 +24,7 @@ import com.intellij.openapi.vfs.VfsUtilCore
 import com.intellij.openapi.vfs.newvfs.impl.VfsRootAccess
 import com.intellij.pom.java.LanguageLevel
 import com.intellij.psi.PsiClassOwner
+import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiJavaFile
 import com.intellij.psi.PsiManager
 import com.intellij.psi.codeStyle.CodeStyleSettings
@@ -58,6 +59,7 @@ import java.util.*
 import kotlin.reflect.full.findAnnotation
 
 abstract class KotlinLightCodeInsightFixtureTestCase : KotlinLightCodeInsightFixtureTestCaseBase() {
+
     private val exceptions = ArrayList<Throwable>()
 
     protected open val captureExceptions = true