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

compiler/testData/asJava/ultraLightClasses/inheritance.java

@@ -0,0 +1,78 @@
+public abstract interface Intf /* Intf*/ {
+  public abstract int v();//  v()
+
+}
+
+public abstract interface IntfWithProp /* IntfWithProp*/ extends Intf {
+  public abstract int getX();//  getX()
+
+}
+
+public abstract class Base /* Base*/ {
+  private int y;
+
+  private int z;
+
+  @org.jetbrains.annotations.Nullable()
+  protected java.lang.Integer v();//  v()
+
+  protected int getZ();//  getZ()
+
+  protected void setZ(int);//  setZ(int)
+
+  public  Base(int);//  .ctor(int)
+
+  public abstract int abs();//  abs()
+
+  public final void nv();//  nv()
+
+  public int getX$light_idea_test_case();//  getX$light_idea_test_case()
+
+  public int getY();//  getY()
+
+  public void setY(int);//  setY(int)
+
+}
+
+public final class Derived /* Derived*/ extends Base implements IntfWithProp {
+  private final int x;
+
+  public  Derived(int);//  .ctor(int)
+
+  public error.NonExistentClass v();//  v()
+
+  public int abs();//  abs()
+
+  public int getX();//  getX()
+
+}
+
+public abstract class AnotherDerived /* AnotherDerived*/ extends Base {
+  private final int x;
+
+  private final int y;
+
+  private final int z;
+
+  protected final void v();//  v()
+
+  protected int getZ();//  getZ()
+
+  public  AnotherDerived(int, int, int);//  .ctor(int, int, int)
+
+  public abstract int getAbstractProp();//  getAbstractProp()
+
+  public abstract void noReturn(@org.jetbrains.annotations.NotNull() java.lang.String);//  noReturn(java.lang.String)
+
+  public int getX$light_idea_test_case();//  getX$light_idea_test_case()
+
+  public int getY();//  getY()
+
+}
+
+final class Private /* Private*/ {
+  public  Private();//  .ctor()
+
+  public boolean getOverridesNothing();//  getOverridesNothing()
+
+}