Add GitHub Action dart-package-analyzer.yml

[cclauss]

@chimon2000 Your review, please?

Output: https://github.com/TheAlgorithms/Dart/runs/1253813888

Related to #86, #87, and #88

Welcome to Dart community

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Dart files are placed inside an existing directory.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[cclauss]

@axel-op Your review please.

[axel-op]

@axel-op Your review please.

This repo is actually not a package (it does not respect the package layout conventions), that's why these checks are failing (there is no pubspec.yaml...)

[cclauss]

Thanks @axel-op

I am not a Dart guy... What is the best way to create a GitHub Action that behaves like
https://github.com/TheAlgorithms/Dart/blob/master/.travis.yml

[axel-op]

@cclauss Try something like this:

name: Analyze

on: [push, pull_request]

jobs:
  analyze:
    runs-on: ubuntu-latest
    
    container: google/dart:2
    
    steps:
      - uses: actions/checkout@v2
      - name: Analyze
        run: dart analyze
      - name: Format
        run: |
          OUTPUT=$(dart format . -o none)
          if [ ! -z "$OUTPUT" ]; then exit 1; fi

[realDuYuanChao]

LGTM

[axel-op]

@cclauss You're welcome!

[cclauss]

@axel-op I changed

OUTPUT=$(dart format . -o none)
if [ ! -z "$OUTPUT" ]; then exit 1; fi
# -->
dart format --set-exit-if-changed .

Merci beaucoup!