Add copy button to markdown code blocks (#17638)

* Add copy button to markdown code blocks

Done mostly in JS because I think it's better not to try getting buttons
past the markup sanitizer.

* add svg module tests

* fix sanitizer regexp

* remove outdated comment

* vertically center button in issue comments as well

* add comment to css

* fix undefined on view file line copy

* combine animation less files

* Update modules/markup/markdown/markdown.go

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

* add test for different sizes

* add cloneNode and add tests for it

* use deep clone

* remove useless optional chaining

* remove the svg node cache

* unify clipboard copy string and i18n

* remove unused var

* remove unused localization

* minor css tweaks to the button

* comment tweak

* remove useless attribute

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/clone_buttons.tmpl

@@ -14,7 +14,7 @@
 	<input id="repo-clone-url" value="{{if $.PageIsWiki}}{{$.WikiCloneLink.SSH}}{{else}}{{$.CloneLink.SSH}}{{end}}" readonly>
 {{end}}
 {{if or (not $.DisableHTTP) (and (not $.DisableSSH) (or $.IsSigned $.ExposeAnonSSH))}}
-	<button class="ui basic icon button poping up" id="clipboard-btn" data-success="{{.i18n.Tr "repo.copy_link_success"}}" data-error="{{.i18n.Tr "repo.copy_link_error"}}" data-content="{{.i18n.Tr "repo.copy_link"}}" data-variation="inverted tiny" data-clipboard-target="#repo-clone-url">
+	<button class="ui basic icon button poping up" id="clipboard-btn" data-content="{{.i18n.Tr "copy_url"}}" data-clipboard-target="#repo-clone-url">
 		{{svg "octicon-paste"}}
 	</button>
 {{end}}