For #4064: Replace prerelease R8 with improved Kotlin coroutines library

[colintheshots]

There are no UI changes here. The only change is replacing the pre-release R8 version with a newer Kotlin coroutines library that no longer uses slow ServiceLoaders on the Main thread.

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

After merge

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

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[codecov-io]

Codecov Report

Merging #7153 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #7153   +/-   ##
=========================================
  Coverage     18.93%   18.93%           
  Complexity      436      436           
=========================================
  Files           288      288           
  Lines         11288    11288           
  Branches       1536     1536           
=========================================
  Hits           2137     2137           
  Misses         8989     8989           
  Partials        162      162

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[mcomella]

@colintheshots What is the expected performance impact for this change? As you mentioned, the new coroutines version has performance improvements and the Dispatcher will no longer be an issue (but it wasn't with the current hack). However, I'm wondering if there will be a performance impact because we're no longer using the newest version of R8 and if that impact will be positive or negative.

Note: an additional assumption of mine is that there are no functional changes.

[mcomella]

No action needed. To state my understanding, in the coroutines CHANGELOG, this fix is:

Avoid ServiceLoader for loading Dispatchers.Main (#1572, #1557, #878, #1606).

sgtm.

[colintheshots]

However, I'm wondering if there will be a performance impact because we're no longer using the newest version of R8 and if that impact will be positive or negative.

I believe it should be fine. The version of R8 we were using was many months old and only slightly newer than the released version. It was so close to making the release that several Google Developer Advocates believed the fix was in the release. There was one other library using a ServiceLoader. We can look for any impact on cold start tonight in the Nimbledroid reports.

[colintheshots]

profile

[hawkinsw]

Scenario	Status	Time (ms)
Cold Startup	success	1770
Enable private browsing	success	440
Turn On Sync	fail	0
Search or enter address	fail	0
Add tab	fail	0
More options	success	360
Disable private browsing	success	410
Text	fail	0
Text	fail	0
Enable private browsing	success	400
Title	success	300
Summary	success	240
Title	success	310
Title	success	200
Summary	success	210
Title	success	190
Title	success	310
Title	success	180
Summary	success	180

[colintheshots]

@mcomella 1770ms seems close to the current Nightly. https://nimbledroid.com/my_apps/org.mozilla.fenix.nightly?p=281aeb00-5223-4746-be25-be2ef36d2bb7#Scenario%20Overview