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)

web_src/js/components/DiffFileTreeItem.vue

@@ -5,7 +5,6 @@
       <!-- Files -->
       <SvgIcon
         v-if="item.isFile"
-        data-position="right center"
         name="octicon-file"
         class="svg-icon file"
       />
@@ -16,7 +15,6 @@
       >{{ item.name }}</a>
       <SvgIcon
         v-if="item.isFile"
-        data-position="right center"
         :name="getIconForDiffType(item.file.Type)"
         :class="['svg-icon', getIconForDiffType(item.file.Type), 'status']"
       />