eslint: use new flat config format (and update deps)

[cstrahan]

This updates eslint (and other dependencies), and switches to the new eslint.config.js flat config format (see https://eslint.org/docs/latest/use/configure/migration-guide).

To preserve the split between .eslintignore and the config file, I've introduced a eslint.ignores.js file, which will be required and included from the generated config, if present.

[cstrahan]

Note that I've changed index.ts (renamed to index.js) to contain the entire config, rather than preserving previous approach where index.ts simply loads and re-exports the config file in the root of the repo.

The reason for this change: typescript-eslint automatically detects the root directory in getTSConfigRootDirFromStack, looking for a file in the callstack with a name matching /^eslint\.config\.(c|m)?(j|t)s$/; so, if index.js requires or imports the config file, then this will make typescript-eslint think that root directory is always the root directory of gts itself.

This is avoided by flipping it around: having gts's eslint.config.js require('./src/index.js').

By having index.js be a javascript file, and requiring that, we ensure that linting the gts repo will work prior to a build (if it was still index.ts, then we'd have to require ./build/src/index.js, which would only exist after compiling).

[cstrahan]

I realized that, in my hastiness, I forgot to commit a couple files; fixed that in the last push.

[jeromy-cannon]

this is great work, did you already file the requested information they put in their contributor page? https://github.com/google/gts?tab=contributing-ov-file

Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution, this simply gives us permission to use and redistribute your contributions as part of the project. Head over to https://cla.developers.google.com/ to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.

[cstrahan]

@jeromy-cannon Thanks!

did you already file the requested information they put in their contributor page?

I've already submitted the CLA, yes.

[cstrahan]

Can I get some direction on desired/needed changes? Happy to do whatever it takes to get this over the finish line.

[jeromy-cannon]

It looks like the last PR was merged over a year ago. I'm not sure if anyone is maintaining this repo. I hope you are able to get your PR through

[tonycoco]

Got moved off this due to some changes internally, but happy to review it. Let me reach out to the team that now maintains it so we can get this merged in ASAP. Thanks for your PR!