Pierce shadowroots on Chromium using caretPositionFromPoint

[Kuuuube]

Fixes #1044

Almost a year ago I wrote this comment #1044 (comment) on our shadow dom issues. Since then, Chromium has gotten caretPositionFromPoint into stable builds and support for the shadowRoots option has been added. There also should have been plenty of time for all maintained Chromium forks to get up to date with this feature.

This allows piercing any shadow root specified by the options. Firefox's implementation pierces all shadow roots by default but we aren't so lucky to get that on Chromium (the people making the w3c spec were against handling it like this w3c/csswg-drafts#9932 (comment)). _findShadowRoots here will get us all the shadow roots within all children of the input element.

The shadow roots are only searched for if caretPositionFromPoint hasnt drilled down to the text to begin with (if we already have the text theres no point in searching for it further). And if the text isn't found, it will start searching for shadow roots at whatever element it ended up drilling down to until it hit shadow dom.

Tested on Firefox 136 and Chromium 133. Unsure if this will blow up on any older versions (testing on kiwi would be a good idea). The feature caretPositionFromPoint is checked for with fallback provided.

Easy test case: https://chromestatus.com/feature/5201014343073792. This site is covered in shadow roots.

[github-actions]

✔️ No visual changes detected by playwright, but flaky tests were detected; please try to fix the tests.