Migrate to ESLint

[DonJayamanne]

We should start using ESLint for all of the new code & just deprecate TS Lint.
Here's my proposal:

• Run ES Lint for all new code (the code is already in place) - core extension have already done this
  • ES Lint will not run for old code
• Run TS Lint for old code
• When an old file is modified, then we run ES Lint on that old modified file
  • This way, anyone making changes to old files will be forced to upgrade everything in that file to eslint
  • Majority of the time it is just ignoring a lot of any usages.

Note:

• This is identical to the approach we took for upgrading the entire code to strict typescript. We started this at least 6months before we decided to update the remainder of the code base.
• Most of the code required is still intact,
• TS Lint has been deprecated, and we knew about this early last year.
• I.e. time to act now, but probably after most of the code has been stabilized

[rchiodo]

How do we distinguish 'old' code from 'new' code in the linter?

[rchiodo]

Oh and why is ES Lint superior? TS Lint seems pretty good so far.

[rchiodo]

This explains the why:
microsoft/TypeScript#29288 (comment)

[DonJayamanne]

How do we distinguish 'old' code from 'new' code in the linter?

This file contains list of old files https://github.com/microsoft/vscode-jupyter/blob/main/.eslintignore