Add ESLint rule for consistent type imports

[phryneas]

This will split up our import statements into import and import type statements, which will hopefully make it easier for bundlers to work with our files, and might remove some accidental runtime import cross-dependencies that might have creeped into our packages.

What do you think - should we do this?

Checklist:

• If this PR contains changes to the library itself (not necessary for e.g. docs updates), please include a changeset (see CONTRIBUTING.md)
• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests

[changeset-bot]

🦋 Changeset detected

Latest commit: d56f26c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@apollo/client	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[alessbell]

I'm in favor of this change: there are the benefits you've mentioned, and the type imports also make the code easier to grok at a glance 🎉

[phryneas]

I talked to Ben yesterday, he's also on board with this. Waiting for input from Jerel on this, and I guess then I'll get this updated & merged :)

[jerelmiller]

I dig it. Thank you!!

[alessbell]

We're only linting **/__tests__/**/*.[jt]sx files on CI right now - we should expand that to include files in src too.