Closes #7656: Add UI tests for Reader View

[AaronMT]

Supports https://testrail.stage.mozaws.net/index.php?/suites/view/3192&group_by=cases:section_id&group_order=asc&group_id=31655 with automated tests

		ID	Title
		C250592	The Reader view toggle appears only when available
		C250588	Enter into reader mode
		C250585	Reader View controls
		C250589	Exit Reader view

[codecov-io]

Codecov Report

Merging #7829 into master will increase coverage by 0.43%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #7829      +/-   ##
============================================
+ Coverage     18.72%   19.15%   +0.43%     
  Complexity      452      452              
============================================
  Files           315      301      -14     
  Lines         12300    11663     -637     
  Branches       1616     1582      -34     
============================================
- Hits           2303     2234      -69     
+ Misses         9798     9244     -554     
+ Partials        199      185      -14

Impacted Files	Coverage Δ	Complexity Δ
.../java/org/mozilla/fenix/ext/ConnectivityManager.kt	14.28% <0%> (-28.58%)	0% <0%> (ø)
...rg/mozilla/fenix/components/toolbar/ToolbarMenu.kt	77.27% <0%> (-18.38%)	0% <0%> (ø)
...java/org/mozilla/fenix/components/FenixSnackbar.kt	0% <0%> (-15.28%)	0% <0%> (ø)
...ttings/advanced/DefaultLocaleSettingsController.kt	80% <0%> (-12.86%)	4% <0%> (-2%)
...fenix/settings/deletebrowsingdata/DeleteAndQuit.kt	57.14% <0%> (-9.53%)	0% <0%> (ø)
app/src/main/java/org/mozilla/fenix/Config.kt	22.58% <0%> (-7.98%)	2% <0%> (ø)
...deletebrowsingdata/DeleteBrowsingDataController.kt	88% <0%> (-7.46%)	0% <0%> (ø)
...g/mozilla/fenix/settings/advanced/LocaleAdapter.kt	0% <0%> (-4.62%)	0% <0%> (ø)
...in/java/org/mozilla/fenix/components/Components.kt	30.55% <0%> (-3.54%)	1% <0%> (ø)
...lla/fenix/collections/SaveCollectionListAdapter.kt	33.33% <0%> (-3.51%)	2% <0%> (ø)
... and 86 more

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[KMaragh]

The reader view is always the second child of the toolbar menu? Does this work if the toolbar is repositioned to the top as well?

[AaronMT]

The hierarchy of the browser toolbar menu remains the same