Differentiate syntax between function definitions and function calls

[axelson]

Goals:

• By default in most themes, function calls should not be highlighted the same
  as function calls
  • Most syntaxes only define function definitions, so most themes highlight
    those definitions with a rather bold color, applying the same coloring to
    all functions calls results in visual noise
• It should still be possible to define custom highlighting for function calls

State of syntax highlighting:

• Textmate syntax highlighting standard (as defined by [1]) defines function
  definitions (entity.name.function) but says nothing about function calls
• Most themes do not support special coloring for function calls
• We can't expect most themes to add special Elixir support

This PR combines portions of #30 and #38 that have similar goals.

PR #30 by itself did not fully accomplish my goals because function calls are
still annotated with entity.name.function.elixir which is highlighted as a
function definition

PR #38 changed the function call names, but it changed it to a non-standard scope.

So in this PR we change the entity.name.function.elixir to
entity.name.function-call.elixir which allows customization, but is a scope
that that does not have default coloring in most themes (while still being
semantically similar).

Also Ruby's syntax uses the similar entity.name.function-call.ruby:
https://github.com/rubyide/vscode-ruby/blob/b232cfd0c96f41ceab72655dcfa17dab40c05562/packages/vscode-ruby/syntaxes/ruby.cson.json#L2243

Related comment: elixir-editors/elixir-tmbundle#179 (comment)

cc: @thiagomajesk, @CaiqueMitsuoka, @chrismccord

[1] https://macromates.com/manual/en/language_grammars

[chrismccord]

beautiful. Thank you!

[thiagomajesk]

Nice one @axelson!
Will this also cover the scenario highlighted here: #22 (comment)?

[axelson]

Nice one @axelson!
Will this also cover the scenario highlighted here: #22 (comment)?

Thanks! Since this doesn't add any new rules, code like say_hello "Caique" will still just be tagged with the scope source.elixir. Ideally we could detect that as a function call, but I'm not sure how difficult that would be (and if it would require any tradeoffs), in any case that would be handled in a separate PR.

[thiagomajesk]

@axelson Indeed!
Do you also think it's necessary to split the original issue to keep up this conversation separately? There are at least a couple more cases in the mix.

[axelson]

Do you also think it's necessary to split the original issue to keep up this conversation separately? There are at least a couple more cases in the mix.

Yeah I think that #22 is too broad, so I'll close it, but please open up individual syntax/grammar improvement issues (or PR's).