For #419: Create shortcuts for private browsing

[jyeontaek]

This PR consists of three PBM features:

1. Long press shortcuts

2. Adding pinned shortcuts

3. Contextual feature recommender for pinned shortcuts

Pull Request checklist

• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests 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

[codecov-io]

Codecov Report

Merging #4948 into master will decrease coverage by 2.2%.
The diff coverage is 7.77%.

@@             Coverage Diff             @@
##             master   #4948      +/-   ##
===========================================
- Coverage     11.61%   9.41%   -2.21%     
+ Complexity      238     206      -32     
===========================================
  Files           243     236       -7     
  Lines          9828    9335     -493     
  Branches       1425    1349      -76     
===========================================
- Hits           1142     879     -263     
+ Misses         8616    8396     -220     
+ Partials         70      60      -10

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/org/mozilla/fenix/home/HomeFragment.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
...ava/org/mozilla/fenix/settings/SettingsFragment.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
...n/java/org/mozilla/fenix/IntentReceiverActivity.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
...a/fenix/components/PrivateShortcutCreateManager.kt	0% <0%> (ø)	0 <0> (?)
...a/org/mozilla/fenix/widget/SearchWidgetProvider.kt	1.33% <0%> (ø)	1 <0> (ø)	⬇️
...pp/src/main/java/org/mozilla/fenix/HomeActivity.kt	7.46% <0%> (-0.23%)	7 <0> (ø)
.../src/main/java/org/mozilla/fenix/utils/Settings.kt	71.55% <17.64%> (-5.18%)	15 <0> (+5)
...la/fenix/home/intent/StartSearchIntentProcessor.kt	90% <80%> (-10%)	4 <3> (ø)
...n/java/org/mozilla/fenix/FenixViewModelProvider.kt	0% <0%> (-100%)	0% <0%> (-2%)
app/src/main/java/org/mozilla/fenix/ext/View.kt	0% <0%> (-100%)	0% <0%> (ø)
... and 46 more

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[NotWoods]

Code looks good but I need to test on my device later. Semi-approved right now :)

[NotWoods]

LGTM! @sblatz please also take a look