The C++ LanguageServer can now find the matching declaration for
variable names, function calls, struct/class types and properties.
When clicking on one of the above with Ctrl pressed, HackStudio will
ask the language server to find a matching declaration, and navigate
to the result in the Editor. :^)
This is a little bit messy but the basic idea is:
Syntax::Highlighter now has a Syntax::HighlighterClient to talk to the
outside world. It mostly communicates in LibGUI primitives that are
available in headers, so inlineable.
GUI::TextEditor inherits from Syntax::HighlighterClient.
This let us to move GUI::JSSyntaxHighlighter to JS::SyntaxHighlighter
and remove LibGUI's dependency on LibJS.
