speedreader: Point to speedreader in settings

[kkuehlz]

We have two options here: (1) Point to
brave://settings?search=speedreader, which will highlight the
Speedreader setting, or (2) or provide a pointer to
brave://settings/appearance. I went with the former because it makes the
setting a bit easier to identify. There isn't a way to link to a
specific setting.

Resolves brave/brave-browser#17216

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

With Speedreader enabled:

• Visit a page which triggers reader mode, e.g. https://jeremykun.com/2014/02/24/elliptic-curves-as-python-objects/
• Click on Speedreader icon at the right of the titlebar
• Click on the "To turn off Speedreader...visit Settings" link in the configuration bubble.
• Confirm the settings page opens scrolled to where the 'Speedreader' enable toggle is visible.

Repeat the test in a locale where the Settings page localises the name of the setting to something other than 'Speedreader', e.g. start Brave with LANGUAGE=ca. Confirm the setting is still highlighted under a different name. Other current options include Amharic, Arabic, Bengali, Farsi, Greek, Kannada, Indonesian, Latvian, Lithuanian, Malay, Norwegian, and Slovenian,

[rillian]

@simonhong What do you think about this version?

[simonhong]

Looks good! 👍🏼

[rillian]

Rebased to address ci build failures.