For #14629 - Enable showing frequently visited sites ON by default

[gabrielluong]

Fixes #14629

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

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[liuche]

Tested this out, turns off nightly flag and sets the default setting to ON

[codecov-commenter]

Codecov Report

Merging #14630 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master   #14630      +/-   ##
============================================
- Coverage     29.76%   29.75%   -0.01%     
+ Complexity     1166     1164       -2     
============================================
  Files           447      447              
  Lines         18135    18134       -1     
  Branches       2355     2355              
============================================
- Hits           5397     5396       -1     
  Misses        12361    12361              
  Partials        377      377              

Impacted Files	Coverage Δ	Complexity Δ
...pp/src/main/java/org/mozilla/fenix/FeatureFlags.kt	100.00% <ø> (ø)	3.00 <0.00> (-1.00)
.../src/main/java/org/mozilla/fenix/utils/Settings.kt	66.81% <100.00%> (ø)	28.00 <0.00> (ø)

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[liuche]

verifyRemoveTopSite
@gabrielluong do you think this breaks now that we have frecency turned on by default? I'll re-run these in any case though.

and probably unrelated:
testStrictVisitSheetDetails

And a ton of unit tests failing for some reason 🤔 https://firefoxci.taskcluster-artifacts.net/euFL0hvkT7eEYOTtyWLzUw/0/public/reports/test/testDebugUnitTest/index.html

[liuche]

This is actually a test failure that needs to be fixed - we try to remove the wikipedia site but since we visit another site we delete the incorrect site.

[gabrielluong]

We need to wait for AC mozilla-mobile/android-components#8325 to get this test to pass.

[liuche]

We still need #14538 (which should be fixed by #14230), but since we need Top Sites for 81, this is fine to land on Nightly.