feat: add Vivaldi support

[normful]

This adds support for Vivaldi -- another Chromium-based browser.

[dhruvmanila]

Can you tell me on which OS have you tested this on?

[normful]

Can you tell me on which OS have you tested this on?

1. For macOS (Darwin), I manually ran :Telescope bookmarks and it worked.
2. For Linux, I didn't actually run it, but instead found Vivaldi's user profile path from people's comments on the Vivaldi support forums:
   • https://forum.vivaldi.net/topic/11994/config-vivaldi/5
3. For Windows, I didn't actually run it, but instead found Vivaldi's user profile path from people's comments on the Vivaldi support forums:
   • https://forum.vivaldi.net/topic/50268/size-of-user-data-folder-very-large

[dhruvmanila]

Thanks!