Framework: Update ESLint configuration to extend shared config

[aduth]

This pull request seeks to update our ESLint configuration to extend a shareable Calypso configuration published as eslint-config-wpcalypso (repository).

Implementation notes:

As a shareable configuration, the base rules should all be defined as errors (specifically to ensure new projects can properly catch these errors before they're introduced). Because Calypso has many lingering warnings, many of the rules have been overridden in our specific configuration to change their severity. I've added a comment noting this, with the hope that these overrides can be removed over time as issues are resolved.

Testing instructions:

There should be no usability impact from these changes.

Verify that linting produces the same results between master and update/eslint-config-external branches.

Test live: https://calypso.live/?branch=update/eslint-config-external

[nylen]

d9f1e1a is amended to remove the unrelated changes to the shrinkwrap file.

With this PR there is no more vars-on-top rule - it should be added to eslint-config-wpcalypso. Other than that, the lint results are the same.

How did you test the lint results? The cleanest way I was able to do it was by modifying bin/run-lint to remove the eslint --quiet flag.

[aduth]

d9f1e1a is amended to remove the unrelated changes to the shrinkwrap file.

Left comment in related conversation at #6539 (comment). I think it's fine to keep the amended commit.

With this PR there is no more vars-on-top rule

That's an eye for detail! This was actually an intended omission, one which I had meant to mention in the original comment. The reason I removed it is because it seems redundant given that we also enable the no-var rule.

How did you test the lint results?

Might not be exactly the same as bin/run-lint, but I ran eslint --ext .js,.jsx client/ server/ test (./node_modules/.bin/eslint if not installed globally).

Looking at bin/run-lint, without arguments it might also run against node_modules, which would be undesirable. Wonder if we should have a default there.

[nylen]

Ah OK, that makes sense. Conflicts with #6539, otherwise good to go 👍

It looks like eslint skips node_modules unless explicitly told not to.

[aduth]

It looks like eslint skips node_modules unless explicitly told not to.

Nice, good to know.

Per the merging of #6539, I separately published v0.2.0 of eslint-config-wpcalypso to drop the wpcalypso/no-lodash-import rule there (changelog), and bumped the dependency in this pull request.