Fix#26731
Almost all "tabindex" in code are incorrect.
1. All "input/button" by default are focusable, so no need to use "tabindex=0"
2. All "div/span" by default are not focusable, so no need to use "tabindex=-1"
3. All "dropdown" are focusable by framework, so no need to use "tabindex"
4. Some tabindex values are incorrect (eg: `new_form.tmpl`), so remove them
Co-authored-by: Giteabot <teabot@gitea.io>
4fdb09de58