[Test] Add regression tests for issues which are fixed in K2

Related issues:
KT-10879, KT-18055, KT-20617, KT-23873
KT-25668, KT-31191, KT-33108, KT-41013
KT-51827, KT-53886, KT-56624, KT-58447
KT-58458, KT-58751, KT-58814, KT-60597
KT-62806, KT-63258, KT-63444, KT-65101
KT-65408, KT-65844, KT-66186

^KT-65926 Fixed

compiler/testData/codegen/box/inference/safeCastWithElvis.kt

@@ -0,0 +1,10 @@
+// WITH_STDLIB
+// IGNORE_BACKEND_K1: JS_IR, JS_IR_ES6, WASM, NATIVE
+// ISSUE: KT-62806
+
+fun <T: Number> foo(x: Number) = x as? T ?: TODO()
+val x: Int? = foo<Int>(1)
+
+fun box(): String {
+    return if (x == 1) "OK" else "Fail: $x"
+}