[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/intersectionWithGenericOnVarargOverride.kt

@@ -0,0 +1,52 @@
+// TARGET_BACKEND: JVM
+
+// FILE: Java1.java
+public class Java1<T> {
+    public void foo(T... a) {};
+}
+
+// FILE: Java2.java
+public interface Java2<T> {
+    public void foo(T... a);
+}
+
+// FILE: 1.kt
+class A<T> : Java1<T>(), Java2<T>
+
+class B<T> : Java1<T>(), Java2<T> {
+    override fun foo(vararg a: T) { }
+}
+
+abstract class C<T> : Java2<T>, KotlinInterface<T>
+
+class D<T> : Java2<T>, KotlinInterface<T> {
+    override fun foo(vararg a: T) { }
+}
+
+interface KotlinInterface<T> {
+    fun foo(vararg a: T)
+}
+
+class E: Java1<Int>(), Java2<Int?>
+
+fun test(a: A<Int>, b: B<Int?>, c: C<Any>, d: D<Any?>, e: E) {
+    a.foo(1, 2)
+    a.foo(1, null)
+    a.foo(null)
+
+    b.foo(1, 2)
+    b.foo(1, null)
+    b.foo(null)
+
+    c.foo(1, 2)
+    c.foo("1", "2", null)
+    c.foo(null)
+
+    d.foo(1, 2)
+    c.foo("1", "2", null)
+    d.foo(null)
+
+    e.foo(1, 2)
+    e.foo(1, null)
+    e.foo(null)
+}