Overwrite elixir syntax with ElixirLS syntax file and configurations

[probably-not]

This copies over the ElixirLS syntax file from https://github.com/elixir-lsp/vscode-elixir-ls/blob/088de57dff9ef24a0273e183a904acdc92274db0/syntaxes/elixir.json (the master branch at time of writing).

I've also updated the package.json with the necessary configurations from https://github.com/elixir-lsp/vscode-elixir-ls/blob/088de57dff9ef24a0273e183a904acdc92274db0/package.json

[lukaszsamson]

Since the syntaxes diverged here's a list of main features added/changes made in ElixirLS version:

• unicode identifier support added
• unicode support in atoms
• reraise keyword
• correct list of operator atoms
• correct matching of defguard as function scope
• removed pre 1.0 keywords
• multiletter uppercase sigils
• corrected textmate scopes for variables
• function call matching
• improvements to @doc and friends

[Blond11516]

Thanks for the update @probably-not!

[Blond11516]

Thanks a lot for the list of changes @lukaszsamson, I'll include them in the changelog!