D.R.Y up Vim modeline expression

[Alhadis]

Description

Fixes:#5347 by updating the Vim Help heuristic with fixes made in #5271 (which should've included heuristics.yml as well… 🤦). I've added a reminder to modeline.rb so something like this doesn't happen again.

(Template removed as it doesn't apply)

[lildude]

I think we also need to add help as an alias for "Vim Help" in order to fix #5347

[Alhadis]

Derp. 🤦🤦 You're right.

At least one of us is paying attention. 😅

[Alhadis]

@lildude We've hit a snag:

  2) Failure:
TestBlob#test_language [/home/runner/work/linguist/linguist/test/test_blob.rb:266]:
textobj-rubyblock.vba.
Expected: "Vim script"
  Actual: "Vim Help File"

This is failing because a VimBall file (see #4412) ends with a help file modeline:

https://github.com/github/linguist/blob/19b3a9bd7d585be8d6459cfab0a51607b2aee68b/samples/Vim%20script/textobj-rubyblock.vba#L215

As the name suggests, VimBalls are the Vim equivalent of a tarball: a concatenation of several files with headers betwixt each blob of data:

https://github.com/github/linguist/blob/19b3a9bd7d585be8d6459cfab0a51607b2aee68b/samples/Vim%20script/textobj-rubyblock.vba#L62-L66

I'm not sure what to do here.

[lildude]

Oh (vim)balls!!!

I'm not sure what to do here.

Yeah, I'm not too sure either. That change is needed in order to fix #5347 (cos of the size of the file) but doing so breaks VimBall detection. I'll need to have a think about it.

[lildude]

Got it!! Vimballs are really easy to find thanks to the first few lines always containing UseVimball.

We can use this to our advantage in the modeline strategy with no extra cost.

I'll push my changes to this branch.