Docs: Use 'key' in 'editor.BlockEdit' filter code examples

[Mamaduka]

What?

PR updates the editor.BlockEdit filter code examples and sets static key for the original BlockEdit component.

Why?

tl;dr - it is just good practice, and most folks don't need to worry about technical details.

The key prevents the BlockEdit component from remounting if its position changes after the initial render. When the key is provided, React will use it as a part of the position instead of the order in the parent component.

Remounting can have unexpected side effects and sometimes even affect the performance.

Testing Instructions

None

[fabiankaegy]

Stupid question on the keys here. Do they not need to be a little more unique? I worry that edit as a key will result in multiple elements with the same key.

🤔

Regardless this is an improvement already

[Mamaduka]

Not in this case, since the filter should only return one block edit component.