SF-2710 Clean up i18n of book-multi-select

[Nateowami]

This change is 

[pmachapman]

The change looks good. This is the first time I have noticed the transloco pipe - it looks like it is more efficient in this case due to using change detection, if I understand the docs correctly?

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @Nateowami)

[Nateowami]

@pmachapman Maybe? I didn't use it for efficiency; I used it because it allowed me to not use the book_select namespace throughout the rest of the file. I would have used the I18nService, but adding that to the component requires changes to the tests, and it wasn't a trivial change, unfortunately.

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @Nateowami)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.05%. Comparing base (771a349) to head (ab40a1d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2430   +/-   ##
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  Coverage   77.05%   77.05%           
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  Files         513      513           
  Lines       29434    29434           
  Branches     4789     4789           
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  Hits        22679    22679           
  Misses       6008     6008           
  Partials      747      747           

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