Feature and motivation

This is a continuation of #14530 point 1: "Discriminated unions". I proposed and implemented Local.Css nested type instead of CssLocator type. My last comment in that already resolved issue was:

I feel new CssLocator("div"); is better, we can make it before v5 if we have strong arguments (types discovery is a good argument).

I was wrong, and now I come with arguments. Actually only one argument. Nested type reserves its name in the parent. Which means we cannot add more members with the same name.

Use cases:

• Static factory: when Selenium Team will have capacity to add more useful methods like Locator.Css("div") it will not be possible, because Css is already defined in Locator class.
• Static singleton: In Script module we have LocalValue.Null class. This is great candidate to be singleton. But we cannot do it because Null name is already reserved by nested type.

Usage example

Before:

new Locator.Css("div");

After:

new CssLocator("div");

And all types with similar pattern.