LSP Toolkit: Add support for delta version of semantic tokens request

[keynmol]

See https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_semanticTokens

This needs to be added to SemanticTokensEncoder companion object (as it doesn't depend on negotiated legend), and should operate directly on two Vector[uinteger]

[ulugbekna]

do you have in mind a real delta or a "fast" one? A fast one being "find common prefix and suffix of two vectors and don't resend those." A fast delta is utilized by rust-analyzer (and now by ocaml-lsp too)