LSP Toolkit datastructures

[keynmol]

There exists perhaps a million reimplementation of the same basic data structures for LSP servers, used both for implementation and testing.

1. Going from offset to a (line, character)
2. Going from (line, character) to offset in the document
3. Getting contents of a line
4. Finding the (line, character) positions of a given offset range
5. Cutout text based on a position range
6. Apply a text edit to given range
7. etc.

It would be good to provide efficient implementations (may be even special cased for platforms!) of these operations, implemented in terms of the LSP structures like Position and Range, so that LSP authors don't reimplement the wheel unnecessarily.

You can see one such implementation here: https://github.com/artempyanykh/marksman/blob/main/Marksman/Text.fs

[kubukoz]

offset -> (line, character) and vice versa are implemented in cats-parse's LocationMap if you want some inspiration :)

Would you say having a "text document manager" would be in scope? vscode-languageserver-node has one, it makes it easier to read a file's contents without having to listen to change events manually.