allow hx-include/disabled-elt/indicator to be optional

[MichaelWest22]

Description

This is a possible improvement to allow hx-include, hx-disabled-elt and hx-indicator to not report errors to the console when a selector finds no elements. Because of how some of these properties can inherit the use of find and similar extended selectors can fail to find any elements when triggered from a different element. When this happens it produces an error message to the console to warn you that it is not working as expected. I think this warning is still useful but it would be nice to have the option to disable the warning for situation where you expect this to happen.

So to allow this I've implemented an option to append a '?' to the end of the selector string which disables the error warning similar to how javascript and regex treat ? at the end as meaning optional.

So for example you can now use hx-include="input?" and if it can not find any inputs to include it will ignore this and not report any errors.

Corresponding issue:
#2895

Testing

Tests added and performed a little manual testing to test and debug the change in a test app

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded

[Telroshan]

Hey, would be interested to have your opinion on #2902 !
I made changes to querySelectorAllExt directly in this one, which technically addresses the same issue since findAttributeTargets uses querySelectorAllExt (+ adds support for multiple extended selectors in hx-trigger's from clause), interested in your thoughts on that matter.

As for the optional change, I would indeed recommend making a separate PR for it, just to keep this down to 1 change to review to the final reviewer (that isn't me), will be easier to get each one approved separately than both at the same time I think!

[MichaelWest22]

Yeah Sorry I should have checked for that PR already being done!!! Your version of the fix is looking good and added a few comments there. Your fix handles one extra case I hadn't considered. So I will strip this PR back to just the optional change so there is less to review.