The version of eslint that we use in most places (8) now spews a warning

about no longer being supported. eslint 9 made a few changes that

require us to update our plugin (which is more a shared configuration

than an actual plugin):
All built-in rules that enforce style have been formally deprecated in

eslint, and actually removed from @typescript-eslint. These now live

in a new plugin, @stylistic/eslint-plugin.
Converting to the new stylistic rules means we can actually simplify our

configuration a bit. Rules that had typescript-specific modes now no

longer require us to disable the JS rule and enable a typescript one,

and we can just include it all in our base configuration.
The indent rule has some known issues with typescript, and it seems

like nobody is terribly willing to rewrite it to fix these. The impact

here seems limited to type parameters for generics. I've added a couple

ignored node types in order to work around this.
For linting within this codebase itself, the eslint configuration now

lives in eslint.config.mjs rather than .eslintrc. This also required

new dependencies for @eslint/eslintrc, @eslint/js, and globals
While I was here, I bumped our babel and typescript dependencies,

why not.

Ran npm build
Ran linting.
Set this up as a link in another package and updated that package to

  use eslint 9. Verified that we got correct linting output.