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

idea/testData/findUsages/java/findJavaMethodUsages/MismatchedAccessor.0.java

@@ -1,6 +1,5 @@
 // PSI_ELEMENT: com.intellij.psi.PsiMethod
 // OPTIONS: usages
-// FIR_COMPARISON
 public class Bar {
     public String getValue() {
         return "value";
@@ -9,4 +8,6 @@ public class Bar {
     public String <caret>getValue(String param) {
         return "value " + param;
     }
-}
+}
+
+// FIR_COMPARISON