Minor accessibility cleanup

[iefremov]

Setup proper accessibility info in our UI elements.

For QA: In MacOS accessibility settings enable "Hover text" and "Typing feedback" and check that hovering speedreader and bookmark buttons (with Cmd pressed to trigger hover text) works as expected. Also check that creating/closing many tabs quickly works as expected.

[stephendonner]

Verified PASSED on Brave	1.24.11 Chromium: 89.0.4389.90 (Official Build) nightly (x86_64)
Revision	62eb262cdaae9ef819aadd778193781455ec7a49-refs/branch-heads/4389@{#1534}
OS	macOS Version 11.2.3 (Build 20D91)

On macOS Big Sur (11.2.3) I tested:

• the Hover text accessibility feature with the Speedreader and Bookmark button UI elements (unable to catch a screenshot of the tooltips, due to timing issue)
• Speak typing feedback
• quickly opening and closing many tabs

Hover text	Speak typing feedback

Leaving issue unverified, so we (others) can check and verify those two features more fully, on Catalina/Mojave, as well, if (probably) needed 👍

---

Verified passed with

Brave | 1.24.81 Chromium: 90.0.4430.93 (Official Build) (x86_64)
-- | --
Revision | 4df112c29cfe9a2c69b14195c0275faed4e997a7-refs/branch-heads/4430@{#1348}
OS | macOS Version 10.15.7 (Build 19H1030)

Confirmed hovertext worked on Speedreader and Bookmark buttons (with CMD selected).
Confirmed able to quickly open/close many tabs/windows with these accessibility features enabled.

Settings used:

Example	Example