[Test] KT-61360: add tests for the IrFakeOverrideBuilder

Add tests for fake overrides with focus on java interoperability

Co-authored-by: Aleksandra Arsenteva <aleksandra.arsenteva@jetbrains.com>

compiler/testData/ir/irText/fakeOverrides/vararg/basicVarargOverride.kt

@@ -0,0 +1,49 @@
+// TARGET_BACKEND: JVM
+
+// FILE: Java1.java
+public class Java1 {
+    public void foo(String... a) {}
+}
+
+// FILE: Java2.java
+public interface Java2 extends KotlinInterface { }
+
+// FILE: 1.kt
+
+class A : Java1()
+
+class B: Java1() {
+    override fun foo(vararg a: String?) { }
+}
+
+abstract class C: Java2 //Kotlin ← Java ← Kotlin
+
+class D: Java2 {        //Kotlin ← Java ← Kotlin
+    override fun foo(vararg a: Any) {}
+}
+
+abstract class E : KotlinInterface2 //Kotlin ← Java ← Kotlin ← Java
+
+class F : KotlinInterface2 {        //Kotlin ← Java ← Kotlin ← Java
+    override fun foo(vararg a: Any) { }
+}
+
+interface KotlinInterface {
+    fun foo(vararg a: Any)
+}
+
+interface KotlinInterface2 : Java2
+
+
+fun test(a: A, b: B, c: C, d: D, e: E, f: F) {
+    a.foo("","1")
+    a.foo(null)
+
+    b.foo("","1")
+    b.foo(null)
+
+    c.foo("","1")
+    d.foo("","1")
+    e.foo("","1")
+    f.foo("","1")
+}