Farble Accept-Language header on subresources

[pilgrim-brave]

Resolves brave/brave-browser#24282

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
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• 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:

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[kjozwiak]

Reproduced the original issue @pilgrim-brave mentioned via brave/brave-browser#24282 (comment) using the following STR/Cases:

• installed 1.44.22 Chromium: 104.0.5112.81
• restarted the browser and ensured that DisableReduceLanguage:Enabled
• double checked and ensured that Prevent sites from fingerprinting me based on my language preferences was enabled via brave://settings/shields
• added several languages via brave://settings/languages
• visited https://dev-pages.brave.software/index.html and opened the DevTools
• under the Network tab, clicked on Disable cache
• refreshed https://dev-pages.brave.software/index.html once again

Farbled	Not farbled	Not farbled

Verification PASSED on Win 11 x64 using the following build(s):

Brave | 1.44.45 Chromium: 104.0.5112.81 (Official Build) nightly (64-bit)
-- | --
Revision | 5b7b76419d50f583022568b6764b630f6ddc9208-refs/branch-heads/5112@{#1309}
OS | Windows 11 Version 21H2 (Build 22000.856)

Used the same STR/Cases outlined above and ensured that accept-language was being farbled on all the files under https://dev-pages.brave.software/index.html as per the following:

Languages selected	Farbled	Farbled	Farbled

Verification PASSED on Samsung S10+ running Android 12 using the following build(s):

Brave | 1.44.49 Chromium: 104.0.5112.81 (Official Build) canary (32-bit)
--- | ---
Revision | 5b7b76419d50f583022568b6764b630f6ddc9208-refs/branch-heads/5112@{#1309}
OS | Android 12; Build/SP1A.210812.016

Languages	FP Disabled	FP Default	FB Strict