feat(lsp): include positionEncodings in default client capabilities

runtime/doc/news.txt

@@ -39,6 +39,12 @@ ADDED FEATURES                                                     *news-added*
 
 The following new APIs or features were added.
 
+• Nvim's LSP client now advertises the general.positionEncodings client
+  capability to indicate to servers that it supports utf-8, utf-16, and utf-32
+  encodings. If the server responds with the positionEncoding capability in
+  its initialization response, Nvim automatically sets the client's
+  `offset_encoding` field.
+
 • Dynamic registration of LSP capabilities. An implication of this change is that checking a client's `server_capabilities` is no longer a sufficient indicator to see if a server supports a feature. Instead use `client.supports_method(<method>)`. It considers both the dynamic capabilities and static `server_capabilities`.
 • |vim.iter()| provides a generic iterator interface for tables and Lua
   iterators |luaref-in|.

runtime/lua/vim/lsp/protocol.lua

@@ -634,6 +634,13 @@ export interface WorkspaceClientCapabilities {
 --- capabilities.
 function protocol.make_client_capabilities()
   return {
+    general = {
+      positionEncodings = {
+        'utf-8',
+        'utf-16',
+        'utf-32',
+      },
+    },
     textDocument = {
       semanticTokens = {
         dynamicRegistration = false,