build: backport "Restore live region changed events for processing by JAWS focus mode"

[alexeykuzmin]

Description of Change

https://chromium-review.googlesource.com/1211508
Original description from the Chromium change

Restore live region changed events for processing by JAWS focus mode

The live region changed events are needed by current versions of JAWS,
which do not process the text inserted events fired by Chrome in all
modes. Specifically, current versions of JAWS processes text inserted
events in virtual cursor mode but not in focus mode. This may change
in future versions of JAWS, and so at some point the live region
changed events may truly become redundant with the text inserted events.

The change Initially landed in M71 and has been backported to M70, but not M69.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Restore live region changed events for processing by JAWS focus mode

[release-clerk]

Release Notes Persisted

Restore live region changed events for processing by JAWS focus mode