Migrate crypto widgets visibility in NTP

[simonhong]

fix brave/brave-browser#19708

Migration is done in the first NTP loading only once.

For new users, all crypto widgets are hidden by default.
For existing users, if current foremost widget is crypto widget,
only it is visible and others are hidden.
After migration, user can control crypto widget's visibility from gallery.

To make all crypto widgets hidden by default, each pref's default
value is not changed. Their default prefs is still "true".
As their visibility are managed by prefs and widget order is managed in local
storage, it's difficult to start migration from c++.

If user has already authed crypto widgets, they will be also visible regardless of position in the widget stack.

Resolves

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:

Test 1 (New user)

1. Launch with clean profile
2. Check all crypto widgets are hidden in NTP widget stack
3. Control their visibility from gallery and check visibility are retained with new NTP or after restarting

Test 2-1 (Existing user)

1. Launch old version brave with existing profile
2. Show some(or all) crypto widgets in stack but set Rewards as a foremost
3. Close old version brave and Launch new Brave
4. Check all crypto widgets are hidden in widget stack

Test 2-2 (Existing user)

1. Launch old version brave with existing profile
2. Show some(or all) crypto widgets in stack and set one of crypto widget as a foremost one
3. Close old version brave and Launch new Brave
4. Check only foremost crypto widget is visible in the stack

Test 2-3 (Existing user that has authed widget)

1. Launch old version brave with existing profile
2. Connect ftx widget
3. Show some(or all) crypto widgets in stack and set one of crypto widget
4. Close old verion brave and Launch new Brave
5. Check ftx widget is not hidden regardless of its position

[petemill]

Nice fast and clean work. 😄

Would be great to squash the commits if you have time.

[simonhong]

Nice fast and clean work. 😄

Would be great to squash the commits if you have time.

Used squash & merge option!

[srirambv]

Verification passed on

Brave	1.34.38 Chromium: 96.0.4664.45 (Official Build) nightly (arm64)
Revision	76e4c1bb2ab4671b8beba3444e61c0f17584b2fc-refs/branch-heads/4664@{#947}
OS	macOS Version 12.0.1 (Build 21A559)

• Verified test plan from pr description
• Verified for clean profile there are not widgets enabled by default except rewards
• Verified for upgrade, when none of the widgets are in foreground, post upgrade only rewards is shown
• Verified when a crypto widget(auth'd or not) is in foreground and rewards is the second one, post upgrade the same order is retained except all other widgets behind rewards is hidden
• Verified when two widgets one auth'd and one that isn't is the foremost widget and rewards is the third one, post upgrade, only the auth'd widget is retained and is the foremost widget and rewards is behind it. unauth'd widget is hidden
• Verified when rewards is the last widget, post upgrade all widgets are hidden and only rewards is shown
• Verified post upgrade only rewards and Brave Talk widgets are retained when Talk is enabled on the older version
• Verified if all widgets are hidden on older version, post upgrade none of them are enabled including rewards
• Verified if rewards is disabled and Binance is the foremost widget, post upgrade only Binance widget is retained and rest all is hidden
• Verified enabling a widget post upgrade is retained between browser restarts