Try enforcing contextual type of array literal elements

Part of #19236 **Code** ```ts const s1: string[] = ["x", 3, null as any]; const s2: string[] = ["x", 3]; ``` **Expected behavior:** * `s1` should be an error * `s2` should have an error span on `3` **Actual behavior:** * `s1` is not an error * `s2` has an error span on `s2`, which makes it impossible to figure out which element is wrong Hypothesis: When checking a contextually-typed array literal, if an element type isn't assignable to the contextual type, issue an error on *that element* and return `unknownType`