New Tab Page: Prompt for Brave Together

[petemill]

• Button in footer always shows
• Prompt (anchored to button) shows like a tooltip until the user manually closes via button.
• (Also adds dir="rtl" as attribute in instead of stylesheet so that it's targetable as a css selector. This is done in most chromium webui now.)

Resolves brave/brave-browser#12776

Button Transitions

Submitter Checklist:

• There is a ticket for my issue.
• Used Github auto-closing keywords in the commit message.
• 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).
• Requested a security/privacy review as needed.

Reviewer Checklist:

• 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:

[petemill]

Apparently this is a new design system-able button style that we can make more shared when the design team iterates a bit more

[zenparsing]

It looks like you are preferring not to add an exported constant to new_tab_types. Do you want to eventually remove the need for that file completely?

[petemill]

Yes just trying to remove 1 layer of boilerplate. I've been using redux-act for Brave Today on the NTP via today_actions.ts and reducers/today, so just continuing that here for anything new.

[zenparsing]

Neat!

[petemill]

Rebased in order to try to fix CI sync errors. Also added a change to storybook in order to provide an option for right-to-left so that we can easily preview what the browser does on the NTP for certain languages. d880de2