Linting: Remove dependency import comments and blank lines repository-wide

[ciampo]

Follow-up to #73396 and this review comment on #81037.

What problem does this address?

We decided to stop using External dependencies, WordPress dependencies, and Internal dependencies comment blocks, but the migration is incomplete.

Earlier work stopped requiring the comments (#73616), added a lint option to forbid them (#74990), and removed them from a few packages (#78573). However:

• About 9,540 dependency comment blocks remain in 5,510 files.
• The coding guidelines still tell contributors to add them.
• Only design-system-mcp, ui, and theme prevent them from being reintroduced.
• Blank lines between import groups are allowed.
• Staged linting does not cover .mjs or .cjs files.

The desired result is one contiguous import block, with no dependency group comments or blank lines between imports. This does not add alphabetization or otherwise change the existing import ordering policy.

For this behavior, the relevant import/order option is newlines-between: "never". newlines-between-types only applies to type-only import groups.

Proposed plan

1. Remove the outdated guidance

   • Stop telling contributors to add dependency group comments.

2. Define the final lint rules

   • Harden and test the existing dependency-group rule's "never" mode.
   • Forbid dependency comments and import blank lines in the base ESLint configuration.
   • Cover *.{js,jsx,ts,tsx,mjs,cjs} files.
   • Preserve meaningful comments and side-effect import order.

3. Replace the strict configuration with bulk suppressions

   • Remove the separate strict ESLint configuration.
   • Run ESLint with --fix first so safely fixable violations are not suppressed.
   • Bulk-suppress remaining legacy violations.
   • Use the existing CI pruning workflow to keep the suppression file current.

4. Remove the legacy violations

   • Fix suppressed violations in reviewable batches.
   • Prune the corresponding suppressions as each batch lands.
   • Add mechanical cleanup commits to .git-blame-ignore-revs.

Done when

• Dependency group comments remain only in lint-rule fixtures.
• Imports have no blank lines between them.
• The base ESLint configuration and CI enforce both rules for all supported files.
• The strict ESLint configuration has been removed.
• Documentation matches the enforced convention.
• No related bulk suppressions remain.

[aduth]

Forbid dependency comments and import blank lines in the strict modified-file configuration.

I think we should get rid of the "strict" configuration and use bulk suppressions instead. #80123 is an example of an ambitious, far-reaching lint rule that has lots of legacy exceptions to make and uses suppressions to achieve this.

Also, if we're currently documenting that contributors should add this, a simple first step would be to remove that documentation.

[ciampo]

@aduth good points, I thought initially that bulk suppressions for those many files would be verbose / too noisy to track, but I like the simplification of removing the strict confit.

Also, I would hope that the majority of the instances would be auto fixable, so we would be able to through that step before resorting to bulk suppression for whatever instances are left.

I've update the issue accordingly 👌

I'll start implementing the migration plan shortly

[ciampo]

Thank you @manzoorwanijk @aduth and @tyxla for helping with this refactor!

A few nice stats:

• 4PRs opened and merged across 2 days
• 5,614 unique files touched
• 603 LOCs added, 33,566 LOCs removed, net of 32,963 LOCs removed (no impact on bundle size)
• Removed roughly 9,540 legacy dependency-comment blocks originally spread across 5,510 files
• Removed all 62 remaining related import/order suppressions
• Repository-wide lint now prevents both dependency-group comments and blank lines between imports.

The recent improvements in AI coding agents enabled a painless refactor; let's take this as an inspiration to keep cleaning up the repo alongside primary feature work.