Add 4DProject and 4DForm extensions to JSON

[vdelachaux]

Description

I would like to add, to complete the 4D programming language, specific extensions, linked to JSON, for the other files used into 4D projects repositories.

Checklist:

• I am associating a language with a new file extension.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?q=extension%3A4DForm+pages+rightMargin+NOT+nothack
      • https://github.com/search?q=extension%3A4DProject+$comment+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/lildude/4DPop-Git/blob/e861aebf5d8f8d9cf44192699932882c84c608e6/Project/4DPop%20Git.4DProject
      • https://github.com/4D-JP/4d-test-read-only-fields/blob/b54a3ce77eefd1e825356b0fdad70b18baf6ed1c/read-only-fields.4dbase/Project/Sources/TableForms/1/Input/form.4DForm
    • Samples license: Both MIT

[Ganbin]

This pull request is more complete than the old one I have made in September 2019 (#4639) as it contains 3 more extensions that are related to 4D Projects.

@pchaigno Can you do another monitoring to see if we get an evolution since the release of the v18 is officially out since January 2018.

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[vdelachaux]

Please could you make a review ?
Thank you for your help.
Vincent

[pchaigno]

Sorry for the long delay here @vdelachaux 🙇‍♂️

[vdelachaux]

I hope you are safe and understand the delay 😷

[pchaigno]

I've just finished counting repositories for the .4DForm extension with Harvester and despite the 1,928 files, it's actually only 80 repositories by 26 users. I'll continue monitoring usage for that extension at #4219.

[Nixinova]

4DForm by itself should be good to go under the new requirements in #5756. the other extensions should be removed.

[lildude]

I've cleaned up and finish off this PR now. I've removed the XML entries as the files are already correctly identified as XML so nothing needs to be done.

I've added samples and update the OP to reflect this.

No longer relevant