feat: add recently used emojis section

[shabicha]

Contributor checklist

• This pull request is on a separate branch and not the main branch
• I have tested my code with the ./gradlew lintKotlin detekt test command as directed in the testing section of the contributing guide

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Description

Added a recently used emoji keyboard functionality, along with a "Recently Used" header, for all InterfaceVariables.kt files for each of the languages.
Changes:

• Added RECENTLY_USED_EMOJI_HEADER to each InterfaceVariables.kt for localized headers
• Added RecentEmojiHelper.kt to persist recently used emojis (checking for duplicates, max emoji values at 30, most recent first)
• Updated GeneralKeyboardIME.kt and KeyboardUIManager.kt to record selections and add "Recently Used" section above existing categories
• Added category strip icon for "Recently Used" in EmojiHelper.kt

Related issue

-Closes #654

[shabicha]

Apologies for the delay @andrewtavis!

[andrewtavis]

No apologies necessary, @shabicha! So great to have this in! I'll add it to the MVP changelog now 😊

[andrewtavis]

@DeleMike would you be able to take an initial look here?

Or also @bhanu-dev82, let us know if you have any availability these days :) We're very much on the home stretch once the final PRs are brought, so getting a bit of support with reviews or testing functionality once we get the -next release- PRs merged would be great!

[andrewtavis]

praise: Checking this with @DeleMike and @angrezichatterbox right now, @shabicha :) All's working really well! We were thinking that we could improve this with a system that checks how often the user users a specific emoji, but this certainly works for the MVP. We can get to more advanced ways of doing this in the future once we have user input 😊