[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.txt

@@ -0,0 +1,73 @@
+class A<T : Any?> : Java1<T>, Java2<T> {
+  constructor() /* primary */ {
+    super/*Java1*/<@FlexibleNullability T?>()
+    /* <init>() */
+
+  }
+
+}
+
+class B<T : Any?> : Java1<T>, Java2<T> {
+  constructor() /* primary */ {
+    super/*Java1*/<@FlexibleNullability T?>()
+    /* <init>() */
+
+  }
+
+  override fun foo(vararg a: T) {
+  }
+
+}
+
+abstract class C<T : Any?> : Java2<T>, KotlinInterface<T> {
+  constructor() /* primary */ {
+    super/*Any*/()
+    /* <init>() */
+
+  }
+
+}
+
+class D<T : Any?> : Java2<T>, KotlinInterface<T> {
+  constructor() /* primary */ {
+    super/*Any*/()
+    /* <init>() */
+
+  }
+
+  override fun foo(vararg a: T) {
+  }
+
+}
+
+class E : Java1<Int>, Java2<Int?> {
+  constructor() /* primary */ {
+    super/*Java1*/<@FlexibleNullability Int?>()
+    /* <init>() */
+
+  }
+
+}
+
+interface KotlinInterface<T : Any?> {
+  abstract fun foo(vararg a: T)
+
+}
+
+fun test(a: A<Int>, b: B<Int?>, c: C<Any>, d: D<Any?>, e: E) {
+  a.foo(a = [1, 2])
+  a.foo(a = [1, null])
+  a.foo(a = [null])
+  b.foo(a = [1, 2])
+  b.foo(a = [1, null])
+  b.foo(a = [null])
+  c.foo(a = [1, 2])
+  c.foo(a = ["1", "2", null])
+  c.foo(a = [null])
+  d.foo(a = [1, 2])
+  c.foo(a = ["1", "2", null])
+  d.foo(a = [null])
+  e.foo(a = [1, 2])
+  e.foo(a = [1, null])
+  e.foo(a = [null])
+}