feat(lsp): support textDocument/onTypeFormatting (#34637)

Implements [on-type
formatting](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.18/specification/#textDocument_onTypeFormatting)
using a `vim.on_key()` approach to listen to typed keys. It will listen
to keys on the *left hand side* of mappings. The `on_key` callback is
cleared when detaching the last on-type formatting client. This feature
is disabled by default.

Co-authored-by: Maria José Solano <majosolano99@gmail.com>

runtime/doc/lsp.txt

@@ -2377,6 +2377,33 @@ set_level({level})                                   *vim.lsp.log.set_level()*
       • {level}  (`string|integer`) One of |vim.log.levels|
 
 
+==============================================================================
+Lua module: vim.lsp.on_type_formatting                *lsp-on_type_formatting*
+
+enable({enable}, {filter})               *vim.lsp.on_type_formatting.enable()*
+    Enables/disables on-type formatting globally or for the {filter}ed scope.
+    The following are some practical usage examples: >lua
+        -- Enable for all clients
+        vim.lsp.on_type_formatting.enable()
+
+        -- Enable for a specific client
+        vim.api.nvim_create_autocmd('LspAttach', {
+          callback = function(args)
+            local client_id = args.data.client_id
+            local client = assert(vim.lsp.get_client_by_id(client_id))
+            if client.name == 'rust-analyzer' then
+              vim.lsp.on_type_formatting.enable(true, { client_id = client_id })
+            end
+          end,
+        })
+<
+
+    Parameters: ~
+      • {enable}  (`boolean?`) true/nil to enable, false to disable.
+      • {filter}  (`table?`) Optional filters |kwargs|:
+                  • {client_id} (`integer?`) Client ID, or `nil` for all.
+
+
 ==============================================================================
 Lua module: vim.lsp.rpc                                              *lsp-rpc*
 

runtime/doc/news.txt

@@ -242,6 +242,8 @@ LSP
 • |vim.lsp.buf.signature_help()| supports "noActiveParameterSupport".
 • Support for `textDocument/inlineCompletion` |lsp-inline_completion|
   https://microsoft.github.io/language-server-protocol/specifications/lsp/3.18/specification/#textDocument_inlineCompletion
+• Support for `textDocument/onTypeFormatting`: |lsp-on_type_formatting|
+  https://microsoft.github.io/language-server-protocol/specification/#textDocument_onTypeFormatting
 
 LUA