Closes #72: Upgrade to SDK 28

[mcomella]

Pull Request checklist

• [x] This PR includes thorough tests or an explanation of why it does not
  • I added unit tests to changed code that won't soon be removed by components implementations (e.g. webView)
• [x] This PR includes a CHANGELOG entry or does not need one
  • Not user facing
• [x] The UI tests are passing after this PR (./gradlew connectedAmazonWebViewDebugAndroidTest)
• [x] I have considered adding QA labels on the associated issue (not this PR; qa-ready or qa-denied)

[mcomella]

Not ready for review: forgot to upgrade support library versions.

[mcomella]

Ready for review.

[codecov-io]

Codecov Report

Merging #233 into master will decrease coverage by 0.04%. The diff coverage is 76.47%.

@@             Coverage Diff              @@
##             master     #233      +/-   ##
============================================
- Coverage      33.9%   33.86%   -0.05%     
- Complexity      358      376      +18     
============================================
  Files           121      123       +2     
  Lines          3224     3417     +193     
  Branches        506      554      +48     
============================================
+ Hits           1093     1157      +64     
- Misses         2030     2159     +129     
  Partials        101      101

Impacted Files	Coverage Δ	Complexity Δ
...ozilla/focus/widget/AccessibleGridLayoutManager.kt	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...illa/focus/toolbar/UrlBoxBackgroundWithProgress.kt	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...w/java/org/mozilla/focus/webview/FirefoxWebView.kt	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
...in/java/org/mozilla/focus/home/HomeTilesManager.kt	5.81% <0%> (-0.07%)	0 <0> (ø)
...main/java/org/mozilla/focus/toolbar/ToolbarText.kt	90% <0%> (-10%)	5 <0> (ø)
app/src/main/java/org/mozilla/focus/ext/Uri.kt	100% <100%> (+9.52%)	0 <0> (ø)	:arrow_down:
.../main/java/org/mozilla/focus/utils/ToastManager.kt	100% <100%> (+100%)	5 <1> (+5)	:arrow_up:
...rc/main/java/org/mozilla/focus/FocusApplication.kt	75% <0%> (-3.27%)	4% <0%> (+1%)
.../java/org/mozilla/focus/browser/BrowserFragment.kt	0% <0%> (ø)	0% <0%> (ø)	:arrow_down:
...org/mozilla/focus/architecture/ViewModelFactory.kt	0% <0%> (ø)	0% <0%> (ø)	:arrow_down:
... and 10 more

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[mcomella]

Unresolved Sentry issue doesn't seem blocking: I'm going to land.