Migrate some SessionManager usage to BrowserStore

[NotWoods]

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

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[csadilek]

Nice! Thanks for starting this. Left two minor comments below and there's a lint error to fix :).

[csadilek]

🚢

[codecov-commenter]

Codecov Report

Merging #10789 into master will increase coverage by 0.01%.
The diff coverage is 21.05%.

@@             Coverage Diff              @@
##             master   #10789      +/-   ##
============================================
+ Coverage     20.45%   20.46%   +0.01%     
+ Complexity      681      680       -1     
============================================
  Files           372      372              
  Lines         15434    15434              
  Branches       2080     2080              
============================================
+ Hits           3157     3159       +2     
+ Misses        11981    11979       -2     
  Partials        296      296              

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/org/mozilla/fenix/FenixApplication.kt	12.16% <0.00%> (-0.09%)	4.00 <0.00> (ø)
...illa/fenix/addons/InstalledAddonDetailsFragment.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...s/deletebrowsingdata/DeleteBrowsingDataFragment.kt	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...zilla/fenix/session/NotificationSessionObserver.kt	83.33% <80.00%> (+40.47%)	2.00 <1.00> (-1.00)	⬆️

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[ekager]

Quick Q: Is it a possible problem that this scope cancel is never called AFAICT? It's not lifecycle aware and we are manually starting it in FenixApplication cc @NotWoods @csadilek

[NotWoods]

Should be fine since we want the notification to stick around

[csadilek]

We have a few store observers / scopes tied to the whole application lifecycle e.g. MigrationTelemetryListener, MigrationPushRenewer. Those never get stopped and don't need to. I guess we could've not assigned the scope and removed the stop method, but yes, it should not be a problem.

[csadilek]

@ekager @NotWoods Actually, we do have a problem here after all! The NotificationSessionObserver is leaking the HomeActivity as it's initialized in HomeActivity.onCreate and uses it as a context. When the HomeActivitiy is re-created, we never cancel the old scope and therefore leak the old HomeActivity. You can reproduce this by enabling "Don't keep activities"...then leak canary gets pretty mad at us :).

@NotWoods I saw you were working on an uplift of this class so we can fix it there? Let's chat in our PR...