Add *.tiltfile extension for Starlark files

[kevinmartin]

Description

Adds *.tiltfile extension to Starlark.

Checklist:

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.tiltfile
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/tilt-dev/tilt/blob/7375e5c286a80c7e9524c35a706025a5830d1e21/web/storybook.tiltfile
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[lildude]

• The new extension is used in hundreds of repositories on GitHub.com

🤨 There are only 70 indexed files in the search results. This is a very very long way from our requirements.

• I have included a real-world usage sample for all extensions added in this PR:

You need to add the file to the PR and also state the license.

I'm going to close this PR as this is a very long way from meeting our usage requirements and it's not likely to meet them any time soon. Feel free to open a new PR when usage meets our requirements.

You can use an override in the meantime.

[kevinmartin]

@lildude Thanks for reviewing this so quickly. I really appreciate the quick turnaround.

Although the *.tiltfile extension currently has few search results, the Tiltfile file name has already been added to the same Starlark language and that has 2.5k+ results.

If anything, I would consider the original addition of Tiltfile as incomplete since it did not consider the *.tiltfile extension. This PR completes the original work from that PR: #4831

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As far as the sample, the PR template asks to specify a URL to the sample, but I see now other PRs are adding samples to the samples/ folder which I'm happy to do.

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Please advise if I can reopen the PR given the above note around the current Tiltfile implementation being incomplete.

[lildude]

Please advise if I can reopen the PR given the above note around the current Tiltfile implementation being incomplete.

It doesn't matter. We evaluate each filename and extension individually so even if that PR attempted to add the .tiltfile extension, it would have have been held up by the lack of usage.