build: migrate eslint config to flat style

[intcreator]

Description

Migrate .eslintrc to esling.config.mjs. Using .mjs so I can use import (.ts configs are still experimental). Fixed a few lint issues that were easy, changed one new lint rule to a warn since it wasn't caught before.

Related Issue

Fixes #899

Motivation and Context

Using the new flat config for Eslint is required for upgrading to 9.0

How Has This Been Tested?

Ran npm run lint and VS Code Eslint plugin many times

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.
• [ ] If my change introduces a breaking change, I have added a ! after the type/scope in the title (see the Conventional Commits standard).

[intcreator]

looks like this won't be able to be merged until we drop support for Node v16

edit: I was able to support Node v16 by downgrading typescript-eslint

[ncb000gt]

:tada: This PR is included in version 3.2.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: