Requiring latitude and longitude to be strictly Number typed impairs ergonomics

[sjmiles]

As we know, JavaScript is weakly typed, and it's not uncommon to end up with numeric data that is in String format. In particular, the native <input> returns only String value, even when set to type="Number".

Whenever possible, it's useful for components to liberally accept Strings where numeric data is required, and perform conversion and the point of requirement.

In this case, the _updateCenter method throws if the latitude or longitude properties are not Number type. It will improve ergonomics if we first cast those properties to Number before checking for isNaN.