Add primary_reading option for "dictionary deinflection" definition type

[stephenmk]

Earlier this year, StefanVukovic99 informed me of a new definition type for supporting dictionary-level deinflections. Currently this syntax allows dictionary authors to redirect from a given term to a different term based upon a single query string. It would be convenient* if an additional primary_reading string could also be included with this redirect, similar to the internal link functionality implemented by khaitruong922 in pull request #1497

* For the dictionaries that I make, at least.

[stephenmk]

@khaitruong922 linked this issue to #1497, but I am actually describing a different feature that is not solved by that pull request.

With the way that deinflection definitions are currently designed, redirections are sometimes not sorted correctly. This could be fixed by allowing a priority_reading parameter to be included in the dictionary deinflection definition type.

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For example, a search for 一かど pulls up the entry for いっかく on top instead of ひとかど.

Example: 一かど

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A search for ひと押し pulls up the entry for いちおし on top instead of ひとおし.

Example: ひと押し

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A search for ひと文字 pulls up the entry for いちもじ on top instead of いちもじ.

Example: ひと文字