fix(dialog): thread blocks during large DOM traversals

[Splaktar]

PR Checklist

Please check that your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

From #9627 (comment):

mdDialog causes thread blocking issues when traversing large DOM trees (in this case, SharePoint 2013) using the walkDOM(element) method. Thread is blocked for approximately 30-40 seconds while aria-hidden attributes are applied.

Issue Number:
Closes #9627.

What is the new behavior?

From #9627 (comment):

mdDialog should open/close without blocking the UI thread due to traversing the DOM tree to apply aria-hidden attributes.

From #9627 (comment)

collect dom elements and then apply any changes instead applying attributes on the fly.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

(cherry picked from commit 44a2d2d)
This retains the fix for live regions from #10807.

As pointed out by @aivaras-b in #10552 (comment), this fix was merged into the release/1.1.1 branch and then never merged to master.

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