Enable TypeScript support in this repo

[bradenmacdonald]

As part of taking over maintainership, I want to be able to use TypeScript to improve the quality of the code in this MFE.

This PR is split into three commits:

1. Turn on TypeScript, set up tsconfig.json and add types for i18n and the constants in src/constants.ts. Updates the CI to do type checking.
2. Update the entire new-sidebars folder to use TypeScript, as an example of converting an entire "thing" to TypeScript
3. Rename all messages.js to messages.ts since none of the "messages" files require any changes to work as TypeScript.

Private ref: MNG-4362

[openedx-webhooks]

Thanks for the pull request, @bradenmacdonald!

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[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.69%. Comparing base (860b3f9) to head (3c78960).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...urseware/course/new-sidebar/common/SidebarBase.tsx	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1459      +/-   ##
==========================================
+ Coverage   88.51%   88.69%   +0.17%     
==========================================
  Files         310      312       +2     
  Lines        5347     5501     +154     
  Branches     1323     1365      +42     
==========================================
+ Hits         4733     4879     +146     
- Misses        597      605       +8     
  Partials       17       17              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[bradenmacdonald]

@farhaanbukhsh another PR for you - no rush :)

[farhaanbukhsh]

@bradenmacdonald this will take some time :)

[farhaanbukhsh]

@bradenmacdonald thanks for this PR I do have a doubt there are a bunch of JS files are we going to migrate them later?

[farhaanbukhsh]

export const WIDGETS: Readonly<{ [k: string]: string }> = {
  DISCUSSIONS: 'DISCUSSIONS',
  NOTIFICATIONS: 'NOTIFICATIONS',
};

@bradenmacdonald I just experimented with this and I found this to be more precise, what do you say?

[bradenmacdonald]

That seems less precise to me? If you do that, the type actually just becomes this, which is basically "any object" - not very useful:

Whereas using the satisfies operator, we get the exactly correct type as a constant:

[farhaanbukhsh]

Are we running the linter for TS and TSX? I can't find the command being updated and changes in eslintrc.

[bradenmacdonald]

Oops, you are right. Fixed with dc39854. Changing .eslintrc shouldn't be needed since it inherits from frontend-build which already configures eslint to support typescript.

[bradenmacdonald]

@farhaanbukhsh Yeah, we can slowly convert the JS to TS. It's too complex to do it all at once. But once this PR is merged, we can convert things as we go, and all new stuff can use TS.