For #10148 - Add basic tab tray implementation without exposing to rest of app

[darkwing]

Fixes #10148

Current view:

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.

After merge

• Milestone: Make sure issues finished by this pull request are added to the milestone of the version currently in development.

To download an APK when reviewing a PR:

1. click on Show All Checks,
2. click Details next to "Taskcluster (pull_request)" after it appears and then finishes with a green checkmark,
3. click on the "Fenix - assemble" task, then click "Run Artifacts".
4. the APK links should be on the left side of the screen, named for each CPU architecture

[codecov-io]

Codecov Report

Merging #9934 into master will decrease coverage by 0.11%.
The diff coverage is 1.04%.

@@             Coverage Diff              @@
##             master    #9934      +/-   ##
============================================
- Coverage     18.97%   18.86%   -0.12%     
  Complexity      532      532              
============================================
  Files           343      344       +1     
  Lines         13944    14039      +95     
  Branches       1869     1882      +13     
============================================
+ Hits           2646     2648       +2     
- Misses        11057    11150      +93     
  Partials        241      241              

Impacted Files	Coverage Δ	Complexity Δ
...pp/src/main/java/org/mozilla/fenix/HomeActivity.kt	9.67% <0.00%> (-0.33%)	10.00 <0.00> (ø)
...c/main/java/org/mozilla/fenix/home/HomeFragment.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
.../java/org/mozilla/fenix/tabtray/TabTrayFragment.kt	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...rc/main/java/org/mozilla/fenix/BrowserDirection.kt	100.00% <100.00%> (ø)	2.00 <0.00> (ø)
...ix/home/sessioncontrol/SessionControlController.kt	72.07% <0.00%> (+0.90%)	0.00% <0.00%> (ø%)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 932fd44...f440665. Read the comment docs.

[ekager]

Why are we using a linear layout for these buttons? Probably better to do a nested constraint in terms of performance?

[ekager]

r+ with some nits