Co-authored-by: Axel <axelhjq@gmail.com>
Co-authored-by: Colin Kennedy <colinvfx@gmail.com>
Co-authored-by: Daiki Noda <sys9kdr@users.noreply.github.com>
Co-authored-by: Evgeni Chasnovski <evgeni.chasnovski@gmail.com>
Co-authored-by: Jean-Jacq du Plessis <1030058+jj-du-plessis@users.noreply.github.com>
Co-authored-by: Juan Giordana <juangiordana@gmail.com>
Co-authored-by: Lincoln Wallace <locnnil0@gmail.com>
Co-authored-by: Matti Hellström <hellstrom@scm.com>
Co-authored-by: Steven Locorotondo <steven.locorotondo@justeattakeaway.com>
Co-authored-by: Yochem van Rosmalen <git@yochem.nl>
Co-authored-by: glepnir <glephunter@gmail.com>
Co-authored-by: ifish <fishioon@live.com>

Co-authored-by: Jesse <github@jessebakker.com>

Problem:
LSP spec uses the term "position encoding" where we say "offset encoding".

Solution:
- Rename it everywhere except `vim.lsp.Client.offset_encoding` (which would be breaking).
- Mention "position encoding" in the documentation for `vim.lsp.Client.offset_encoding`.

- Partition the handlers in vim.lsp.handlers as:
  - client to server response handlers (RCS)
  - server to client request handlers (RSC)
  - server to client notification handlers (NSC)

  Note use string indexes instead of protocol.methods for improved
  typing in LuaLS (tip: use hover on RCS, RSC or NSC).

* deprecate old signatures
* move to new str_byteindex/str_utfindex signature
* use single-underscore name (double-underscore is reserved for Lua itself)

- Also fix `vim.validate()` for PUC Lua when showing errors for values
  that aren't string or number.