[FIR] Set status.isOverride for fake overrides

Even though SO may not be correct
overrides sometimes, it feels more
natural to treat fake overrides as...
well, "overrides". And without it
we'd need to make the code in
`FirOverrideChecker` less intuitive.

compiler/testData/asJava/lightClasses/lightClassByPsi/delegatingToInterfaces.fir.java

@@ -15,6 +15,9 @@ public abstract interface Base /* Base*/ {
 public final class BaseImpl /* BaseImpl*/ implements Base {
   private final int x;
 
+  @java.lang.Override()
+  public final int getX();//  getX()
+
   @java.lang.Override()
   public void printMessage();//  printMessage()
 
@@ -22,8 +25,6 @@ public final class BaseImpl /* BaseImpl*/ implements Base {
   public void printMessageLine();//  printMessageLine()
 
   public  BaseImpl(int);//  .ctor(int)
-
-  public final int getX();//  getX()
 }
 
 public final class Derived /* Derived*/ implements Base {