Move helpers to be prefixed with gt- (#22879)

As discussed in #22847 the helpers in helpers.less need to have a
separate prefix as they are causing conflicts with fomantic styles

This will allow us to have the `.gt-hidden { display:none !important; }`
style that is needed to for the reverted PR.

Of note in doing this I have noticed that there was already a conflict
with at least one chroma style which this PR now avoids.

I've also added in the `gt-hidden` style that matches the tailwind one
and switched the code that needed it to use that.

Signed-off-by: Andrew Thornton <art27@cantab.net>

---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/diff/section_unified.tmpl

@@ -27,7 +27,7 @@
 				{{end}}
 				{{$inlineDiff := $section.GetComputedInlineDiffFor $line $.root.locale -}}
 				<td class="lines-escape">{{if $inlineDiff.EscapeStatus.Escaped}}<a href="" class="toggle-escape-button" title="{{template "repo/diff/escape_title" dict "diff" $inlineDiff "locale" $.root.locale}}"></a>{{end}}</td>
-				<td class="lines-type-marker"><span class="mono" data-type-marker="{{$line.GetLineTypeMarker}}"></span></td>
+				<td class="lines-type-marker"><span class="gt-mono" data-type-marker="{{$line.GetLineTypeMarker}}"></span></td>
 				{{if eq .GetType 4}}
 					<td class="chroma lines-code blob-hunk">{{/*
 						*/}}{{template "repo/diff/section_code" dict "diff" $inlineDiff "locale" $.root.locale}}{{/*