Migrate core/index.js to Typescript

[yiwen101]

What is the purpose of this pull request?

• [ ] Documentation update
• [ ] Bug fix
• [ ] Feature addition or enhancement
• [ ] Code maintenance
• [ ] DevOps
• [ ] Improve developer experience
• [ ] Others, please explain:

Overview of changes: Working on #1913; quite trivial changes.

Anything you'd like to highlight/discuss:

Testing instructions:

Proposed commit message: (wrap lines at 72 characters) Migrate core/index.js to Typescript

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Checklist: :ballot_box_with_check:

• [ ] Updated the documentation for feature additions and enhancements
• [ ] Added tests for bug fixes or features
• [ ] Linked all related issues
• [ ] No unrelated changes

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Reviewer checklist:

Indicate the SEMVER impact of the PR:

• [ ] Major (when you make incompatible API changes)
• [ ] Minor (when you add functionality in a backward compatible manner)
• [ ] Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 51.11%. Comparing base (c268733) to head (370b3ba).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2482 +/- ## ======================================= Coverage 51.11% 51.11% ======================================= Files 124 124 Lines 5355 5355 Branches 1152 1152 ======================================= Hits 2737 2737 Misses 2328 2328 Partials 290 290 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[kaixin-hc]

@yiwen101 - please revert the merge commit 😅

[yiwen101]

@yiwen101 - please revert the merge commit 😅

sorry, I must have accidentally hit "update with merge" someday😅.

[itsyme]

LGTM!

[github-actions[bot]]

@itsyme Each PR must have a SEMVER impact label, please remember to label the PR properly.