refactor(lsp): rename offset_encoding to position_encoding #31286

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`.

runtime/lua/vim/lsp/_changetracking.lua

@@ -18,14 +18,14 @@ local M = {}
 ---
 ---   None: One group for all clients
 ---   Full: One group for all clients
----   Incremental: One group per `offset_encoding`
+---   Incremental: One group per `position_encoding`
 ---
 --- Sending changes can be debounced per buffer. To simplify the implementation the
 --- smallest debounce interval is used and we don't group clients by different intervals.
 ---
 --- @class vim.lsp.CTGroup
 --- @field sync_kind integer TextDocumentSyncKind, considers config.flags.allow_incremental_sync
---- @field offset_encoding "utf-8"|"utf-16"|"utf-32"
+--- @field position_encoding "utf-8"|"utf-16"|"utf-32"
 ---
 --- @class vim.lsp.CTBufferState
 --- @field name string name of the buffer
@@ -46,7 +46,7 @@ local M = {}
 ---@return string
 local function group_key(group)
   if group.sync_kind == protocol.TextDocumentSyncKind.Incremental then
-    return tostring(group.sync_kind) .. '\0' .. group.offset_encoding
+    return tostring(group.sync_kind) .. '\0' .. group.position_encoding
   end
   return tostring(group.sync_kind)
 end
@@ -72,7 +72,7 @@ local function get_group(client)
   end
   return {
     sync_kind = sync_kind,
-    offset_encoding = client.offset_encoding,
+    position_encoding = client.offset_encoding,
   }
 end
 
@@ -310,7 +310,7 @@ local function send_changes_for_group(bufnr, firstline, lastline, new_lastline,
     -- The contents would further change and startline/endline may no longer fit
     local changes = incremental_changes(
       buf_state,
-      group.offset_encoding,
+      group.position_encoding,
       bufnr,
       firstline,
       lastline,