Normalize issue labels with other dart-lang/ repos

Hi - we're normalizing issue labels with the other dart-lang/ repos (in order to have fewer labelling systems to know about, to make it easier to move labels between repos, and to make it possible to answer questions like how many P1 issues are open against our repos).

Here are the differences between the labels in this repo and the canonical dart-lang (https://github.com/dart-lang/.github/labels) labels:

```
(rename) [P0 critical]: rename => P0, color => #D93F0B, description => "A serious issue requiring immediate r..."
(rename) [P1 high]: rename => P1, color => #f9c0b4, description => "A high priority bug; for example, a s..."
(rename) [P2 medium]: rename => P2, color => #FBCA04, description => "A bug or feature request we're likely..."
(rename) [P3 low]: rename => P3, color => #FEF2C0, description => "A lower priority bug or feature request"
(rename) [Resolution: duplicate]: rename => closed-duplicate, color => #686868, description => "Closed in favor of an existing report"
(rename) [Resolution: invalid]: rename => closed-invalid, color => #686868, description => "Closed as we don't believe the report..."
(rename) [Resolution: wontfix]: rename => closed-not-planned, color => #686868, description => "Closed as we don't intend to take act..."
(rename) [Resolution: works as intended]: rename => closed-as-intended, color => #686868, description => "Closed as the reported issue is expec..."
(rename) [State: blocked]: rename => status-blocked, color => #444444, description => "Blocked from making progress by anoth..."
(rename) [State: help wanted]: rename => contributions-welcome, color => #C2E0C6, description => "Contributions welcome to help resolve..."
(rename) [State: needs info]: rename => status-needs-info
(rename) [Type: bug]: rename => type-bug, color => #fff9e3, description => "Incorrect behavior (everything from a..."
(rename) [Type: enhancement]: rename => type-enhancement, color => #fff9e3, description => "A request for a change that isn't a bug"
(rename) [Type: question]: rename => type-question, color => #fff9e3, description => "A question about expected behavior or..."
(update) [autosubmit]: color => #1D76DB
(update) [needs-info]: color => #444444, description => "Additional information needed from th..."
(add) [closed-cannot-reproduce]: #686868 "Closed as we were unable to reproduce the reported issue"
(add) [closed-obsolete]: #686868 "Closed as the reported issue is no longer relevant"
(add) [closed-stale]: #686868 "Closed as the issue or PR is assumed stale."
(add) [good first issue]: #C2E0C6 "A good starting issue for contributors (issues with this label will appear in /contribute)"
(add) [type-code-health]: #fff9e3 "Internal changes to our tools and workflows to make them cleaner, simpler, or more maintainable"
(add) [type-documentation]: #fff9e3 "A request to add or improve documentation"
(add) [type-infra]: #fff9e3 "A repository infrastructure change or enhancement"
(add) [type-ux]: #fff9e3 "A user experience or user interface related issue"
(consistency) [Area: delete request]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: discontinue request]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: implementation]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: metadata needed]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: package analysis]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: package docs]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: pana-related]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: search]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: site feedback]: avoid spaces; use lowercase-dashes to join words
(consistency) [Area: stackdriver error report]: avoid spaces; use lowercase-dashes to join words
(consistency) [Customer-Flutter]: avoid upper case; use lowercase names
(consistency) [dev: tool]: avoid spaces; use lowercase-dashes to join words
(consistency) [dev: tool - packages]: avoid spaces; use lowercase-dashes to join words
(consistency) [S0 critical]: avoid spaces; use lowercase-dashes to join words
(consistency) [S1 high]: avoid spaces; use lowercase-dashes to join words
(consistency) [S2 medium]: avoid spaces; use lowercase-dashes to join words
(consistency) [S3 low]: avoid spaces; use lowercase-dashes to join words
(consistency) [Type: quality]: avoid spaces; use lowercase-dashes to join words
(consistency) [v2 Design]: avoid spaces; use lowercase-dashes to join words
```

Above:
- `rename` means that our labelling tool will rename the existing dart-lang/pub-dev label
- `update` means it will change some property about the label
- `add` means it'll create a new label
- `consistency` means that an existing label doesn't meet our style guidelines (the tool will take no action on this label)

For the `consistency` issues, we need to either manually rename the label, remove it (if there are no or few uses), or decide that we're ok w/ the style difference. Often we want to keep the label but should prefix or rename it (i.e., add an `area-` prefix or similar).

To run this tool yourself:

- clone https://github.com/dart-lang/ecosystem
- `cd pkgs/repo_manage`
- `dart pub get`
- `dart bin/report.dart labels-update --dry-run dart-lang/pub-dev`

And, to have the tool update the labels, run `dart bin/report.dart labels-update --apply-changes dart-lang/pub-dev`.