Upgrade from Chromium 90 to Chromium 91.

[mkarolin]

Upgrade from Chromium 90 to Chromium 91

https://chromium.googlesource.com/chromium/src/+log/90.0.4430.93..91.0.4472.19/?pretty=fuller&n=10000

QA tests:
This is a major Chromium version bump, please do full passes.

Desktop Affected areas:

1. Version number display in UI
2. Components update
3. Settings and Extensions UI pages
4. Page info bubble
5. Avatar button
6. Ad notifications

Consider testing with 91.0.4471.38 (#15641)

[stephendonner]

Verified PASSED using

Brave	1.26.19 Chromium: 91.0.4472.38 (Official Build) nightly (64-bit)
Revision	8155e7afab5d695cf0e028f4d77203287523cda9-refs/branch-heads/4472_35@{#6}
OS	Windows 10 OS Version 2009 (Build 21376.1)

I ran through the manual test run (thanks to @GeetaSarvadnya for the help!) and it PASSED: #15682

I also tested the affected areas listed:

1. Version number display in UI
2. Components update
3. Settings and Extensions UI pages
4. Page info bubble
5. Avatar button
6. Ad notifications

Found no new issues other than those logged below:

Issues found (not all by me):

• Nightly CR91 major bump is missing 3 sections in Privacy and security #15808 - Nightly CR91 major bump is missing 3 sections in Privacy and security - FIXED, landed in master
• Cr91 follow-up: Fix omnibox selection color.  #15690 - Omnibox selection color - FIXED, landed in master
• tab search button has weird hover/press effect #15670 - tab-search hover - FIXED, landed in master
• Toggling Live caption via media-playback button dynamically downloads Google SODA components #15864 - Toggling Live caption via media-playback button dynamically downloads Google SODA components - under investigation
• Crash in invalid-read when relaunching after setting new language as Brave's default #15763 - Crash in invalid-read when relaunching after setting new language as Brave’s default - nobody else has yet been able to repro; I think we can keep investigating post-merge
• tab hover cards with C91 #15795 - tab hover cards are back, with C91, needs final decision, I think?
• Web Store link in brave://extensions is underlined and wrong color #15807 - Web Store link in brave://extensions is underlined and wrong color - should fix, but can wait post-Cr91-merge to master
• Consider pulling in some options from Chromium's Accessibility settings page #15844 - Consider pulling in some options from Chromium’s Accessibility settings page - needs vetting, especially as relates to 15864

[kjozwiak]

Labeling as QA/No and adding release-notes/exclude in favour of #15800.