Use data-tooltip-content for tippy tooltip (#23649)

Follow:
* #23574
* Remove all ".tooltip[data-content=...]"

Major changes:

* Remove "tooltip" class, use "[data-tooltip-content=...]" instead of
".tooltip[data-content=...]"
* Remove legacy `data-position`, it's dead code since last Fomantic
Tooltip -> Tippy Tooltip refactoring
* Rename reaction attribute from `data-content` to
`data-reaction-content`
* Add comments for some `data-content`: `{{/* used by the form */}}`
* Remove empty "ui" class
* Use "text color" for SVG icons (a few)

templates/repo/blame.tmpl

@@ -41,7 +41,7 @@
 							</td>
 							<td class="lines-blame-btn">
 								{{if $row.PreviousSha}}
-									<a href="{{$row.PreviousShaURL}}" class="tooltip" data-content='{{$.locale.Tr "repo.blame_prior"}}'>
+									<a href="{{$row.PreviousShaURL}}" data-tooltip-content='{{$.locale.Tr "repo.blame_prior"}}'>
 										{{svg "octicon-versions"}}
 									</a>
 								{{end}}