fix(content): only collect required translations

[yin1999]

Summary

Trying to fix and as a part of #8301

Gather all translation would slow down the static document build in translated-content. Only gather the translations of the incoming slug might be a better idea.

Problem

After we migrating to ESM, the PR-test ci in translated-content would spend more than 25 seconds to build a single document (as in most of PRs, the number of changed documents is only 1). The most of time during a build is spent on
gathering all translations (as metioned in #8301).

Solution

Try to gather the translations of a required slug only, this should save most of the time for build a single document.

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Using a locale build of yari to check the build time.

Run yarn build files/en-us/learn/common_questions/web_mechanics/what_is_a_web_server/index.md
and node node_modules/@mdn/yari/build/cli.js files/zh-tw/learn/common_questions/web_mechanics/what_is_a_web_server/index.md to build document.

Screenshots

Before

~16 seconds are used to build a single document.

After

~1 seconds are used to build a single document.

run yarn start in content

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[LeoMcA]

Nice optimisation! Logic looks solid, just some syntax comments:

[yin1999]

Thanks for the suggestions @LeoMcA, I've tested again for building the translated document:

[LeoMcA]

Fantastic, thanks for this!