For #4991:Ensured deleteSelectedBookmarks deletes all selected bookmarks

[mcarare]

Moved the deletion to a CoroutineScope(IO) to decouple from fragment lifecycle
Used local val tempStorage to keep reference to bookmarkStorage of outside class
Ran deletions with awaitAll to avoid concurrency issues on storage

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.

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[codecov-io]

Codecov Report

Merging #5559 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #5559      +/-   ##
============================================
- Coverage     14.04%   14.04%   -0.01%     
  Complexity      311      311              
============================================
  Files           255      255              
  Lines         10414    10418       +4     
  Branches       1507     1508       +1     
============================================
  Hits           1463     1463              
- Misses         8840     8844       +4     
  Partials        111      111

Impacted Files	Coverage Δ	Complexity Δ
...ozilla/fenix/library/bookmarks/BookmarkFragment.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
...va/org/mozilla/fenix/onboarding/FenixOnboarding.kt	0% <0%> (ø)	0% <0%> (ø)	⬇️
...g/mozilla/fenix/crashes/CrashReporterController.kt	94.11% <0%> (ø)	6% <0%> (ø)	⬇️

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[sblatz]

Looks good!