[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/generics/basicGenericMethodsOverride.kt.txt

@@ -0,0 +1,42 @@
+class A : Java1 {
+  constructor() /* primary */ {
+    super/*Java1*/()
+    /* <init>() */
+
+  }
+
+}
+
+class B : Java1 {
+  constructor() /* primary */ {
+    super/*Java1*/()
+    /* <init>() */
+
+  }
+
+  override fun <T : Any> bar(): T? {
+    return CHECK_NOT_NULL<Nothing>(arg0 = null)
+  }
+
+  override fun <T : Any> foo(a: T?) {
+  }
+
+}
+
+fun test(a: A, b: B) {
+  val k: Int = a.bar<@FlexibleNullability Int?>() /*!! Int */
+  val k2: Int? = a.bar<Int?>()
+  val k3: Any = a.bar<@FlexibleNullability Any?>() /*!! Any */
+  val k4: Nothing = a.bar<@FlexibleNullability Nothing?>() /*!! Nothing */
+  a.foo<@FlexibleNullability Int?>(a = 1)
+  a.foo<Nothing?>(a = null)
+  a.foo<@FlexibleNullability Int?>(a = null)
+  a.foo<@FlexibleNullability List<Nothing?>?>(a = listOf<Nothing?>(element = null))
+  val k5: Int? = b.bar<Int>()
+  val k7: Any? = b.bar<Any>()
+  val k8: Nothing? = b.bar<Nothing>()
+  b.foo<Int>(a = 1)
+  b.foo<Nothing>(a = null)
+  b.foo<Int>(a = null)
+  b.foo<List<Nothing?>>(a = listOf<Nothing?>(element = null))
+}