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 #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 :white_check_mark:

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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