Refactor manifesto initialization to push property localization down

[cbeer]

From #3482:

A recent change in the Manifesto library made it possible to pass a list of languages (in descending order of preference) to the PropertyValue.getValue and PropertyValue.getValues methods, instead of relying on a single default locale that would be set when parsing the manifest. This allows for a better user experience, since we can now dynamically respond to changes in the user's language preferences without having to re-parse the manifest. Additionally, we can make use of the browser's language preferences to better match the user's language abilities.

This does the same thing as #3482, without introducing new redux state or a new selector parameter, in order to maintain API compatibility for downstream plugins. Instead, this PR:

• introduces a LocaleContext and locale-context aware IIIFResourceLabel for rendering e.g. manifest, canvas, etc labels appropriately, replacing a lot of piece-meal label functions
• ensures components within a companion window include that context when calling selectors (to get the getLocale/getManifestLocale to work right... this is somewhat unfortunate, but probably less weird if we started to use hooks or more extensive use of context like Use context to pass the window id around #3661 (and a companion-window equivalent))
• Clean up styling for the companion window locale picker to make it more like the workspace language selector

This can be tested at https://deploy-preview-3871--mirador-dev.netlify.app/__tests__/integration/mirador/i18n.html

Fixes #3470

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (593e81b) 92.53% compared to head (6933a52) 92.54%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3871   +/-   ##
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  Coverage   92.53%   92.54%           
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  Files         203      205    +2     
  Lines        3579     3582    +3     
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+ Hits         3312     3315    +3     
  Misses        267      267           

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