IR Scripting: allow to specify nullable types for provided props...

but only explicitly. This does not fix a breaking change described in
#KT-52120, because it seems the correct behavior, but it allows
to "workaround" the problem by specifying nullability explicitly.
Also improve handling of nullable bindings in JSR-223.
#KT-49173 fixed
#KT-51213 fixed

libraries/scripting/jsr223-test/test/kotlin/script/experimental/jsr223/test/KotlinJsr223ScriptEngineIT.kt

@@ -261,6 +261,10 @@ obj
             put("boundValue", 100)
         })
         Assert.assertEquals(111, result2)
+
+        engine.put("nullable", null)
+        val result3 = engine.eval("bindings[\"nullable\"]?.let { it as Int } ?: -1")
+        Assert.assertEquals(-1, result3)
     }
 
     @Test
@@ -280,6 +284,10 @@ obj
             put("boundValue", 100)
         })
         Assert.assertEquals(111, result2)
+
+        engine.put("nullable", null)
+        val result3 = engine.eval("nullable?.let { it as Int } ?: -1")
+        Assert.assertEquals(-1, result3)
     }
 
     @Test