feat: add downvote power slider with confirmation

[th7nder]

Fixes #2126

Changes

• Added downvote slider analogically to the upvote's one
• Updated Slider component indicator

Test plan

• [ ] Make sure you have 'Enable slider' checked in settings or your rank is Dolphin or higher
• [ ] Select a random post and go to the comments' section
• [ ] Click dislike

Demo (optional)

[Sekhmet]

I think it might be a good idea to always display slider (for upvotes & downvotes) no matter user rank. Otherwise we will have to default to some downvote percent which is not ideal.