Improve experience when using ruleset in repo with mixed JS, TS, and Angular code

In this Skyline PR I enabled linting for the JS files in an Angular project. This situation is common because of config files like karma.conf.js and .eslintrc.js. I hit a couple small bumps that would be nice to address in this repo.

1. Had to manually modify the repo's .eslintrc.js to use the JavaScript ruleset for files matching *.js. We should either document this as our recommended approach or change our Angular and TS rulesets to apply to JS files too.
2. I had to modify angular.json lintFilePatterns to include *.js since the npm run lint command called ng lint. We should document this.
3. A few rules failed on the default karma.conf.js generated by Angular. I chose to suppress those rules. In another case we chose to fix them (see discussion in linked PR). It would be nice to settle on a preferred approach and include guidance in our repo since most projects will likely hit the same errors.
   • if we choose to suppress, we could change our ruleset to do this automatically for karma.conf.js
   • if we choose to fix, we could add notes on each rule's docs or create StackOverflow posts explaining how to fix

Review the repository's .eslintrc.js, angular.json, and generated karma.conf.js, then read the linked Skyline pull request and its discussion. Determine and document the preferred handling for mixed JS and TypeScript Angular projects, including lintFilePatterns and the reported Karma rule failures; done means the guidance or ruleset behavior is settled and documented.