feat: add config for gnls

Add support for Microsoft's GN language server [1].

[1] https://github.com/microsoft/gnls

Signed-off-by: Nick Diego Yamane <nickdiego@igalia.com>

Author: nickdiego

lsp/gnls.lua

@@ -0,0 +1,19 @@
+---@brief
+---
+--- https://github.com/microsoft/gnls
+---
+--- Microsoft's language server for GN build files.
+---
+--- Assuming there is a `gnls` script somewhere in your `$PATH`, containing
+--- for example:
+---
+--- ```shell
+--- GNLS_SRC_DIR=</path/to/gnls>
+---
+--- exec node ${GNLS_SRC_DIR}/build/server.js $@
+--- ```
+return {
+  cmd = { 'gnls', '--stdio' },
+  filetypes = { 'gn' },
+  root_markers = { '.gn', '.git' },
+}