Migrated from JSHint to ESLint

[Nishthajain7]

Fixes #1540

Changes: Updated the preprocessing lint step to use ESLint instead of JSHint.

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[khanniie]

Hi! Thank you so much for the contribution! If this is regarding the codemirror 5 to 6 migration, the subissue we published was actually regarding the js linter used within the Editor/stateUtils.js file. I do think the approach is correct, it would be great if you could move the changes to that file!