[FIR IDE] Add Fir lightclasses tests and fix FindUsages tests

compiler/tests-common/tests/org/jetbrains/kotlin/asJava/AbstractCompilerLightClassTest.kt

@@ -36,12 +36,12 @@ abstract class AbstractCompilerLightClassTest : KotlinMultiFileTestWithJava<Kotl
         val expectedFile = KotlinTestUtils.replaceExtension(wholeFile, "java")
         val allowFrontendExceptions = InTextDirectivesUtils.isDirectiveDefined(wholeFile.readText(), "// ALLOW_FRONTEND_EXCEPTION")
 
-        LightClassTestCommon.testLightClass(
-            expectedFile,
+        val actual = LightClassTestCommon.getActualLightClassText(
             wholeFile,
             { fqname -> findLightClass(allowFrontendExceptions, environment, fqname) },
             LightClassTestCommon::removeEmptyDefaultImpls
         )
+        KotlinTestUtils.assertEqualsToFile(expectedFile, actual)
     }
 
     override fun createTestModule(

compiler/tests-common/tests/org/jetbrains/kotlin/asJava/LightClassTestCommon.kt

@@ -7,7 +7,6 @@ package org.jetbrains.kotlin.asJava
 
 import com.intellij.openapi.util.io.FileUtil
 import com.intellij.psi.PsiClass
-import com.intellij.psi.impl.compiled.ClsElementImpl
 import junit.framework.TestCase
 import org.jetbrains.kotlin.asJava.PsiClassRenderer.renderClass
 import org.jetbrains.kotlin.asJava.classes.KtLightClass
@@ -19,12 +18,11 @@ object LightClassTestCommon {
     private val SUBJECT_FQ_NAME_PATTERN = Pattern.compile("^//\\s*(.*)$", Pattern.MULTILINE)
     private const val NOT_GENERATED_DIRECTIVE = "// NOT_GENERATED"
 
-    fun testLightClass(
-        expectedFile: File,
+    fun getActualLightClassText(
         testDataFile: File,
         findLightClass: (String) -> PsiClass?,
         normalizeText: (String) -> String,
-    ) {
+    ): String {
         val text = FileUtil.loadFile(testDataFile, true)
         val matcher = SUBJECT_FQ_NAME_PATTERN.matcher(text)
         TestCase.assertTrue("No FqName specified. First line of the form '// f.q.Name' expected", matcher.find())
@@ -32,8 +30,7 @@ object LightClassTestCommon {
 
         val lightClass = findLightClass(fqName)
 
-        val actual = actualText(fqName, lightClass, normalizeText)
-        KotlinTestUtils.assertEqualsToFile(expectedFile, actual)
+        return actualText(fqName, lightClass, normalizeText)
     }
 
     private fun actualText(fqName: String?, lightClass: PsiClass?, normalizeText: (String) -> String): String {