Remove dependency on the Rewards extension

[zenparsing]

Resolves brave/brave-browser#22423

High-level overview:

The goal of this change is to ensure that all Rewards features can be run without loading the Rewards built-in extension. Currently, the Rewards extension is used to:

• Display the Rewards action button with a badge containing a notification count or creator "checkmark".
• Display the Rewards panel.
• Display the Brave Talk opt-in panel.
• Record and store information about the creator associated with a given tab.

In this PR:

• RewardsTabHelper is modified to take responsibility for recording tab/creator activity.
• A desktop-only browser helper RewardsPanelCoordinator is added to route "panel requests" to the appropriate handler. Code that previously loaded the Rewards extension and called BraveActionAPI::ShowActionUI have been refactored to use this coordinator.
• A new native button class BraveRewardsActionView is added to display the Rewards icon button.
• A MojoBubbleWebUIController is added to display the Rewards panel (rewards_panel_ui.h).
• The Rewards panel front-end is modified to work in both extension and WebUI contexts.
• The Rewards panel front-end is modified to allow displaying the Brave Talk opt-in.
• A feature flag is introduced (named "Use WebUI Rewards Panel") that, when enabled, will cause the browser to display the Rewards panel using WebUI and the Rewards button using BraveRewardsActionView. When enabled, the Rewards extension should not need to be loaded.

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:

Regression Testing

The following cases should be tested for regressions with the feature flag off:

• All strings on the Rewards panel are displayed properly.
• Publisher info is displayed properly in the panel for a variety of publishers.
• After enabling Rewards from the NTP, the panel is opened with the Rewards tour displayed.
• Adaptive captcha is displayed correctly when the user clicks on the Adaptive captcha tooltip.
• On the adaptive captcha UI, the support URL is opened correctly.
• Grant captchas can be opened from the NTP and from the Rewards page.
• Button "checkmark" state and publisher info is correct for Greaselion publishers.
• The Rewards panel can be opened from the settings page when the user has not enabled Rewards.

With the feature flag on, the following cases should be tested in addition to the cases above:

• For a variety of publishers, the Rewards icon shows the correct "checkmark" badge.
• The Rewards icon shows the correct notification count badge when there are Rewards notifications.
• When the Rewards icon is hidden in settings, the Rewards icon does not appear.
• When the Rewards icon is hidden in settings, the panel can still be opened from the NTP and Rewards page as indicated above.
• When in a "private" context (i.e. a private window or tor window), the Rewards icon does not appear.

[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