Added Vale to site checks

[atsansone]

No description provided.

[MaryaBelanger]

To run vale:

1. brew install vale
2. vale sync
3. vale path/to/file.md

---

Tested, runs fine.

$ vale src/community/who-uses-dart.md

 src/community/who-uses-dart.md
 1:1    warning     Try to keep the Flesch–Kincaid  Readability.FleschKincaid        
                    grade level (9.44) below 8.                                      
 1:1    warning     Try to keep the LIX score       Readability.LIX                  
                    (45.22) below 35.                                                
 1:1    warning     Try to keep the Automated       Readability.AutomatedReadability 
                    Readability Index (9.93) below                                   
                    8.                                                               
 1:1    warning     Try to keep the Coleman–Liau    Readability.ColemanLiau          
                    Index grade (10.82) below 19.                                    
 1:1    warning     Try to keep the SMOG grade      Readability.SMOG                 
                    (10.86) below 10.                                                
 1:1    warning     Try to keep the Flesch reading  Readability.FleschReadingEase    
                    ease score (58.27) above 70.                                     
 1:1    warning     Try to keep the Gunning-Fog     Readability.GunningFog           
                    index (10.78) below 10.                                          
 14:37  warning     'many' is a weasel word!        write-good.Weasel                
 15:21  suggestion  Try to avoid using 'are'.       write-good.E-Prime               
 17:1   suggestion  Try to avoid using 'you're'.    write-good.E-Prime               
 25:2   suggestion  Spell out 'IDEAS', if it's      Google.Acronyms                  
                    unfamiliar to the audience.                                      
 25:8   suggestion  Spell out 'FOR', if it's        Google.Acronyms                  
                    unfamiliar to the audience.                                      
 26:4   error       Did you really mean             Vale.Spelling                    
                    'endcomment'?                                                    

✖ 1 error, 8 warnings and 4 suggestions in 1 file.

---

A couple things I would like to see:

1. I wish the warnings about various readability grades contained links to the definition / pointers about how to improve that in the CL output. If you find the file, they do provide a link to more info on the grade there.
2. "weasel word" would also be a nice thing to link and define. What does that mean? The write-good/Weasel file does not contain a definition (can imagine it would not be self explanatory for ESL users).
3. Over time, we should be customizing this a lot to our style requirements, like removing things that are not vital. Excessive notifications will be a deterrent to actually implementing what Vale suggests.

---

Concern:

1. The above example shows me 1 error / 8 warnings / 4 suggestions, but the VS Code integration shows be different warnings. This is the case with all the other pages I tested too. Probably just a config issue on my end, but should keep an eye out for that.

[MaryaBelanger]

Hard to test everything, but this PR isn't forcing anyone to use it and we can improve it/pare down through our own regular use, so lgtm with that in mind

[MaryaBelanger]

Decided to actually fit it to the google style guide before merging

[sfshaza2]

Woah! @atsansone, before merging a new tool like this, we need to see it staged, try it out, and make a team decision. Have you staged this?

[sfshaza2]

On further thought, I'm closing this PR for now. We need a lot more research before adding a tool like this. We should probably get @khanhnwin involved if we feel it's important enough. (To be honest, given my current understanding, I don't feel like I need this. Hence the research and testing.)

[dart-github-bot]

Visit the preview URL for this PR (updated for commit be8f7e8):

https://dart-dev--pr4231-vale-implementation-rsgx3g06.web.app

[atsansone]

Moved to dart-lang/site-shared#223 per conversation with @parlough .