feat(lsp): support textDocument/documentColor

test(lsp): add tests form `vim.lsp.document_color`

src/gen/gen_vimdoc.lua

@@ -278,6 +278,7 @@ local config = {
       'inlay_hint.lua',
       'tagfunc.lua',
       'semantic_tokens.lua',
+      'document_color.lua',
       'handlers.lua',
       'util.lua',
       'log.lua',