Better logic for showing user feed/public activity elements (#4189)

There are a few changes of template logic which defines when which elements should be shown on profile page. The motivation is to have the elements when needed and don't when they're not relevant.

## Changes

### RSS button

Now displayed if:
* feeds are enabled
AND one or more of:
* the current user is an admin
* the current user is viewing their profile
* the activity is publicly available

So, basically in cases when the .rss feed actually contains any events. Before this change this button was constantly shown and was giving an empty feed if it was unavailable.

### Public activity tab

The tab is displayed if:
* the current user is an admin
* the current user is viewing their profile
* the activity is publicly available
* the current tab is this exact tab, for example, in case it was accessed by adding `?tab=activity` to the URL, so that the UI is not broken w/o a highlighted tab

So, this tab is not displayed when it's not going to contain any information, but still can be accessed.

### Banner "This user has disabled the public visibility of the activity."

For admins:
* always show the big blue banner to warn that sharing a screenshot of this publicly is bad idea

For self:
* always display a little note about the current visibility status with a "Change" link

For others:
* only display a little note to explain why the activity is not shown

### Heatmap and activity feed

Elements are only displayed when relevant, instead of keeping empty leftovers, for easier testing. This template change is also covered by test. **Everything in this Changes section is covered by test unless I forgot something.**

## Preview

There's obviously too many states to screenshot, here are highlights:

![](https://codeberg.org/attachments/47559531-9bcd-46c0-90d4-8b51512da752)
_Warning admin for why they're seeing the information_

![](https://codeberg.org/attachments/3107bf62-955b-4fe5-bce3-6305a928afe1)
_Viewing self - private_

![](https://codeberg.org/attachments/afb63ead-fb0b-4fc7-9d8b-c6c09e9ae62b)
_Viewing self - public_

![](https://codeberg.org/attachments/df3c090a-7490-4827-b33b-771fd4fa0a9f)
_Don't have access to the information_

![](https://codeberg.org/attachments/2dd2b0ac-2fe0-4453-aa4b-e91fd08f4411)
_The tab is not shown when the activity can't be accessed_

![](https://codeberg.org/attachments/ed4c61de-b3b7-4523-b92b-bc76e1d8b7c5)
_Can't access the RSS feed_

![](https://codeberg.org/attachments/5a27f2be-d79c-4fb4-85a5-758348398f1b)
_Can access the RSS feed_

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/4189
Reviewed-by: Otto <otto@codeberg.org>

options/locale/locale_en-US.ini

@@ -679,11 +679,16 @@ overview = Overview
 block = Block
 unblock = Unblock
 user_bio = Biography
-disabled_public_activity = This user has disabled the public visibility of the activity.
 email_visibility.limited = Your email address is visible to all authenticated users
 show_on_map = Show this place on a map
 settings = User settings
 
+disabled_public_activity = This user has disabled the public visibility of the activity.
+public_activity.visibility_hint.self_public = Your activity is visible to everyone, except for interactions in private spaces. <a href="%s">Configure</a>.
+public_activity.visibility_hint.admin_public = This activity is visible to everyone, but as an administrator you can also see interactions in private spaces.
+public_activity.visibility_hint.self_private = Your activity is only visible to you and the instance administrators. <a href="%s">Configure</a>.
+public_activity.visibility_hint.admin_private = This activity is visible to you because you're an administrator, but the user wants it to remain private.
+
 form.name_reserved = The username "%s" is reserved.
 form.name_pattern_not_allowed = The pattern "%s" is not allowed in a username.
 form.name_chars_not_allowed = Username "%s" contains invalid characters.