Fix selection error when backwards selections cover fields

[jonathonherbert]

What does this change?

Fixes an error where backwards selections that extend beyond a field are passed into the field view, causing range errors.

The errors are largely harmless – they're a no-op on the state and do not halt the outer editor – but they're causing some noise in our downstream CMS's error reporting.

There's a question as to whether fields should be aware of selections that cover them entirely. I don't think we've seen a use case yet, but we could map and clamp the selection values, rather than just ignoring, if we wanted that behaviour.

How to test

• The new unit tests should pass. The commit history shows the failure, then the pass.
• Try adding a backwards selection across an element. You should not see red ink in the console:

[rhystmills]

Think this may need a rebase now but I am happy to review as soon as possible.

[jonathonherbert]

Thanks @rhystmills, just done that. (Now we no longer use semantic-release in this library, perhaps it's worth turning off squash and merge, which IIUC makes conflicts more likely.)

[rhystmills]

Makes sense as a fix, and all tests passing 👍