Make sure autocomplete triggers are regex safe

[notnownikki]

Description

Fixes: #10781

Make sure autocomplete triggers are made safe for use in regex.

How has this been tested?

Install and test the autocomplete example from #10781

Types of changes

Bug fix

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[notnownikki]

@georgeh @mkaz If this is an acceptable fix, we might want to carry this as a patch until the next release.

[ellatrix]

Tbh, I do not remember writing anything like this, but maybe I did. Others have collaborated on the Autocomplete component in the few-times-squashed 78d1254, but this may very well me my mistake, if so, apologies! :)

[ellatrix]

Looks good!

[notnownikki]

Thanks for the review :) To be honest I just pinged you because 1) your name was on the merge, and 2) reviews from you are always appreciated!