Improve RSS feed icons (#28368)

- The RSS Feed icons were placed in a proper button, so that it does
  not look "inconsistent". This also makes the problem of the button
  being improperly aligned go away.
- The icon that shows on user profiles has not been modified because
  of a lack of better implementation ideas.
- Where applicable, the RSS Feed icon was put directly next to the
  Follow button (right menu), as both functionalities effectively
  share the same purpose.
- Despite the attempt at achieving less inconsistency, a conscious
  decision to not add any text to those buttons was made, opting for
  tooltips instead. "Make it present, but not too annoying."
- A special exception was made for the Releases pages (which contains
  text, not a tooltip), where an RSS feed would be particularly
  beneficial to users.

The fact that the RSS functionality is explicitly optional was taken
into account, and these improvements were made with public-facing
instances (where the feature works best) in mind.

templates/repo/header.tmpl

@@ -25,9 +25,6 @@
 							<span class="ui basic label">{{ctx.Locale.Tr "repo.desc.template"}}</span>
 						{{end}}
 					</div>
-					{{if $.EnableFeed}}
-						<a class="rss-icon gt-ml-3" href="{{$.RepoLink}}.rss" data-tooltip-content="{{ctx.Locale.Tr "rss_feed"}}">{{svg "octicon-rss" 18}}</a>
-					{{end}}
 				</div>
 				{{if $.PullMirror}}
 					<div class="fork-flag">{{ctx.Locale.Tr "repo.mirror_from"}} <a target="_blank" rel="noopener noreferrer" href="{{$.PullMirror.RemoteAddress}}">{{$.PullMirror.RemoteAddress}}</a></div>
@@ -55,6 +52,12 @@
 							</div>
 						</form>
 					{{end}}
+					{{if $.EnableFeed}}
+					{{/* An extra div-element is not necessary here, as this button does not secretly contain two buttons. */}}
+					<button class="ui compact small basic button" data-url="{{$.RepoLink}}.rss" data-tooltip-content="{{ctx.Locale.Tr "rss_feed"}}">
+						{{svg "octicon-rss" 16}}
+					</button>
+					{{end}}
 					<form method="post" action="{{$.RepoLink}}/action/{{if $.IsWatchingRepo}}un{{end}}watch?redirect_to={{$.Link}}">
 						{{$.CsrfTokenHtml}}
 						<div class="ui labeled button" {{if not $.IsSigned}}data-tooltip-content="{{ctx.Locale.Tr "repo.watch_guest_user"}}"{{end}}>