[lsp-server] handle syntax highlighting at the LSP level

## Current Behavior (if applicable)

All of our code highlighting is provided by static grammar files that are only available to vscode clients

## Desired Behavior

We should lean on the LSP to generate code highlitghing rules for us programatically

https://github.com/microsoft/vscode-languageserver-node/pull/367

this will make our code highlighting logic far more testable

yes this would lead to retiring the syntax extension