Closes #394 - Trusted Web Activities

[NotWoods]

Depends on mozilla-mobile/android-components#4440 and #4914

Adds support for Trusted Web Activities in Fenix nightly and debug.

Here are some apps using Trusted Web Activities we can test with:

• https://play.google.com/store/apps/details?id=com.tigeroakes.insightfulenergy
• https://play.google.com/store/apps/details?id=com.appspot.pwa_directory
• https://play.google.com/store/apps/details?id=br.com.quintoandar.inquilinos

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
• 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

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".

[codecov-io]

Codecov Report

Merging #5391 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #5391      +/-   ##
============================================
- Coverage     14.37%   14.35%   -0.03%     
  Complexity      320      320              
============================================
  Files           257      257              
  Lines         10588    10604      +16     
  Branches       1551     1551              
============================================
  Hits           1522     1522              
- Misses         8940     8956      +16     
  Partials        126      126

Impacted Files	Coverage Δ	Complexity Δ
...in/java/org/mozilla/fenix/components/Components.kt	37.03% <0%> (-12.97%)	1 <0> (ø)
...a/org/mozilla/fenix/components/IntentProcessors.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
.../org/mozilla/fenix/customtabs/CustomTabsService.kt	0% <0%> (ø)	0 <0> (ø)	⬇️

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[sblatz]

This looks good to me, but I'm still not seeing pull to refresh on these. Is that expected?

[NotWoods]

We don't yet support pull to refresh. That's depended on the corresponding AC feature, which needs to be updated now that GeckoView has added the necessary dependency.

We're going to ask the QA team to look at this before merging as well.