Add advanced semantic highlighting to the `ruby-lsp`

[vinistock]

Improve our existing semantic highlighting to address more complex Ruby syntax.

• [ ] Method and block arguments
• [ ] Punctuation (e.g.: the namespace separator :: or the pipes in a block argument are sometimes highlighted incorrectly without semantic support)
• [ ] Class vs constant
• [ ] self in front of singleton method definitions and the accompanying dot
• [ ] Add the private modifiers to methods, allowing us to highlight them slightly differently than public methods

We can also enhance the highlighting of syntax that is related to a specific tool, such as Sorbet or Rails. For example,

• [ ] Sorbet signature declarations
• [ ] Other Sorbet inline type annotations, such as T.let
• [ ] Rails callbacks
• [ ] Rails associations

Etc

• [ ] Document how to create a theme

Additionally, the specification supports some performance related improvements we can explore. There are two existing options (maybe implementing both is a good idea too)

• Implementing semantic tokens delta and refresh. This means we have to maintain in memory (inside our Document store) the current semantic tokens for a file and only return the difference between the previous response and the current one (indicating which tokens were deleted and which ones were added)
• Implement semantic tokens for a range. This one is considerably easier than delta and refresh, it's just a matter of returning only the tokens for the given visible range of the document to avoid flickering. In short, it's a new request endpoint where we could simply re-use our semantic tokens implementation and filter tokens that are outside of range

Documentation: https://microsoft.github.io/language-server-protocol/specification#textDocument_semanticTokens