[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/intersectionOnVarargOverride.kt

@@ -0,0 +1,48 @@
+// TARGET_BACKEND: JVM
+
+// FILE: Java1.java
+public class Java1 {
+    public void foo(Object... a) {}
+}
+
+// FILE: Java2.java
+public interface Java2 {
+    public void foo(String... a);
+}
+
+
+// FILE: 1.kt
+abstract class A : Java1(), Java2
+
+class B : Java1(), Java2 {
+    override fun foo(vararg a: String) { }
+}
+
+abstract class C : Java2, KotlinInterface
+
+class D: Java2, KotlinInterface {
+    override fun foo(vararg a: Any) { }
+
+    override fun foo(vararg a: String?) { }
+}
+
+interface KotlinInterface {
+    fun foo(vararg a: Any)
+}
+
+fun test(a: A, b: B, c: C, d: D) {
+    a.foo(1, 2)
+    a.foo("1", "2")
+    a.foo(null)
+
+    b.foo(1, 2)
+    b.foo("1", "2")
+    b.foo(null)
+
+    c.foo(1, 2)
+    c.foo("1", "2")
+    c.foo(null)
+
+    d.foo(1, 2)
+    d.foo(null)
+}