Add class static initialization block example

[hamishwillee]

This adds examples for class static initialization block, added in FF93 . This will appear in docs here: mdn/content#9281

There is a lot that might be shown. This primarily just shows the syntax for declaring a block, and that it can access/declare a property using the this.

[Rumyra]

So my theories on tests failing are:

• No new line at end of file (see review)
• JSlint actually can't parse a static block(?)

I'm not sure of the implications of merging this if the second point is true 🤔

[hamishwillee]

As per the discussion you had with Will:

Looks like it might be eslint/eslint#15016 ? If so I think we should disable eslint for this example, but remember to enable it again when support for static lands in eslint.

I am presuming no action from me. Happy to do this, but would need instruction on how.