Change Language IDs to comply with guidelines (Closes #86)

[zolrath]

@axelson Here you are! I'm not sure of the full extent of testing this that should occur or if we should combine its merger with pull requests on other popular packages supporting html.eex to reduce the impact of the change.

The language identifier guidelines state that language ids should be lowercase and contain no spaces.
https://code.visualstudio.com/docs/languages/identifiers#_new-identifier-guidelines

This mostly is a port of changes that were never merged for the old vscode-elixir definition.
timmhirsens/vscode-elixir#114

The largest impact of this change is that other extensions that rely on the current identifier would have to be changed for support to continue.

Fixes #86

[axelson]

Thanks! ❤️ This looks like a good change to bring the extension into alignment with VSCode guidelines. Hopefully the migration won't be too difficult for users. I'll hold off on merging until we write a short guide on adjusting configuration to match, if it is short enough it can live in ElixirLS's changelog, if it is longer it can be a new .md file in this repo.

Here's some related issues that we may additionally want to drop a comment on:

• Fix EEx support (for elixir/phoenix) tailwindlabs/tailwindcss-intellisense#54

Related issues:

• Note: HTML (EEx) change affects related settings JakeBecker/vscode-elixir-ls#134
• Update EEx identifiers to match vscode-elixir-ls stefanjarina/vscode-eex-snippets#1

A PR should also be filed against:

• https://github.com/stefanjarina/vscode-eex-snippets

[zolrath]

vscode-tailwindcss now has support for html-eex
https://github.com/bradlc/vscode-tailwindcss/pull/111/files

and I've submitted a pull request for vscode-eex-snippets
stefanjarina/vscode-eex-snippets#5

[zolrath]

As far as things to put in the changelog/document things that people may have copy/pasted into their settings and forgotten about that they should remember to update would include:
If you're using Emmet for HTML expansion be sure to include the new Language Id in your settings.json file.

Ctrl+Shift+P or Cmd+Shift+P and type Preference: Open Settings (JSON)
Add or edit your emmet.includedLanguages to include the new Language Id:

"emmet.includeLanguages": {
    "html-eex": "html"
}

[axelson]

Thank you very much for the upgrade guide and for making those PR's! I'm going to go ahead and merge this now 🎉

[stefanjarina]

Hello all, just FYI, pull request for this merged to stefanjarina/vscode-eex-snippets.
Also new version 0.0.7 already available in marketplace.
Thank you a lot for PR :-)