Rename Str2html to SanitizeHTML and clarify its behavior (#29516)

Str2html was abused a lot. So use a proper name for it: SanitizeHTML

And add some tests to show its behavior.

templates/repo/commit_page.tmpl

@@ -276,7 +276,7 @@
 				<span class="text grey" id="note-authored-time">{{TimeSince .NoteCommit.Author.When ctx.Locale}}</span>
 			</div>
 			<div class="ui bottom attached info segment git-notes">
-				<pre class="commit-body">{{.NoteRendered | Str2html}}</pre>
+				<pre class="commit-body">{{.NoteRendered | SanitizeHTML}}</pre>
 			</div>
 		{{end}}
 		{{template "repo/diff/box" .}}

templates/repo/issue/view_content/comments.tmpl

@@ -162,7 +162,7 @@
 				</span>
 				<div class="detail">
 					{{svg "octicon-git-commit"}}
-					<span class="text grey muted-links">{{.Content | Str2html}}</span>
+					<span class="text grey muted-links">{{.Content | SanitizeHTML}}</span>
 				</div>
 			</div>
 		{{else if eq .Type 7}}

templates/repo/settings/webhook/base_list.tmpl

@@ -10,7 +10,7 @@
 <div class="ui attached segment">
 	<div class="ui list">
 		<div class="item">
-			{{.Description | Str2html}}
+			{{.Description | SanitizeHTML}}
 		</div>
 		{{range .Webhooks}}
 			<div class="item truncated-item-container">