Problem: filetype: various ignore are not recognized
Solution: detect rg/docker/npm/vvsce ignore files as 'gitgnore' filetype
(Wu, Zhenyu)
Not only prettier, but many programs also support ignore files (like rg,
docker, npm, vscode). So use the gitignore filetype for them due to same syntax
closes: vim/vim#164288cbe2e0a0a
Co-authored-by: Wu, Zhenyu <wuzhenyu@ustc.edu>