replace twig-language-server with twiggy-language-server

[jannisborgers]

This replaces the old twig-language-server from the Modern Twig VSCode extension with the more up-to-date twiggy-language-server from the Twiggy VSCode extension, while keeping gbprod/tree-sitter-twig as the extension’s grammar and fixes the extension’s failure to install and run the language server.

PS: I also put the grammars directory and extension.wasm in .gitignore, they are generated by the extension on install. I’m not sure about excluding the grammar, but the .wasm is excluded in other extensions, so I put it there.