Fir2Ir: enable IR-based fake override builder

Invert the logic of IR/FIR2IR-based generators: change the CLI argument
to -Xuse-fir-fake-override-builder, test directive to
USE_FIR_BASED_FAKE_OVERRIDE_GENERATOR, etc.

The changes in test data caused by using IR fake override builder by
default are in the subsequent commit.

 #KT-61514

compiler/testData/ir/irText/declarations/fakeOverrideModality.kt

@@ -1,5 +1,4 @@
 // FIR_IDENTICAL
-// ENABLE_IR_FAKE_OVERRIDE_GENERATION
 // TARGET_BACKEND: JVM
 
 open class Base

compiler/testData/ir/irText/declarations/internalStdlibOverride.kt

@@ -1,6 +1,5 @@
 // FIR_IDENTICAL
 // WITH_STDLIB
-// ENABLE_IR_FAKE_OVERRIDE_GENERATION
 // KT-64692
 
 // test data differs - no getOrDefault in AbstractMap for non-jvm.
@@ -11,4 +10,4 @@ class MyMap : AbstractMap<Int, Int>() {
 
     // clash with stdlib internal function
     fun containsEntry(entry: Map.Entry<*, *>?) = false
-}
+}

compiler/testData/ir/irText/declarations/kt65236.kt

@@ -1,5 +1,4 @@
 // FIR_IDENTICAL
-// ENABLE_IR_FAKE_OVERRIDE_GENERATION
 // TARGET_BACKEND: JVM
 
 // FILE: J.java
@@ -29,4 +28,4 @@ class E : D() {
 
 fun foo(x : I) {
     x.foo()
-}
+}

compiler/testData/ir/irText/declarations/kt65432.kt

@@ -1,10 +1,7 @@
-// WITH_STDLIB
-// ENABLE_IR_FAKE_OVERRIDE_GENERATION
-// SEPARATE_SIGNATURE_DUMP_FOR_K2
-// ^ Value parameters in fake overrides generated by K1 and K2 are different
-
 // WITH_REFLECT
 // TARGET_BACKEND: JVM_IR
+// SEPARATE_SIGNATURE_DUMP_FOR_K2
+// ^ Value parameters in fake overrides generated by K1 and K2 are different
 
 // FILE: Java1.java
 public class Java1 extends KotlinClass { }
@@ -14,4 +11,4 @@ import java.util.ArrayList
 
 class A : Java1()
 
-open class KotlinClass : ArrayList<Int>()
+open class KotlinClass : ArrayList<Int>()