Detached DOM: Commands.addQuery()

[BlueWinds]

What would you like?

As part of the Detached DOM work, we need to implement "queries", which are commands that function in a different way from existing cypress commands - they are synchronous, idempotent, and aren't responsible for their own retry loop.

I'm starting work with .get() and .as() - these are some of the most complicated commands in Cypress (encompassing as they do "getting elements from the DOM" and aliases, which are strangely complex for a simple-sounding concept).

Why is this needed?

Have to start somewhere. I started at the deep end, so that I can encounter any issues with my approach immediately rather than later in the process.

Other

This PR is again the develop branch - unlike the previous iteration of this work, it should be safe to release to users as-is (not a breaking change).