Fix and restyle menu on code line (#15913)

* Fix and restyle menu on code line

* fix multiline and more tweaks

* move to separate files

* remove has-context-menu class

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/js/code/linebutton.js

@@ -0,0 +1,11 @@
+import {svg} from '../svg.js';
+
+export function showLineButton() {
+  if ($('.code-line-menu').length === 0) return;
+  $('.code-line-button').remove();
+  $('.code-view td.lines-code.active').closest('tr').find('td:eq(0)').first().prepend(
+    $(`<button class="code-line-button">${svg('octicon-kebab-horizontal')}</button>`)
+  );
+  $('.code-line-menu').appendTo($('.code-view'));
+  $('.code-line-button').popup({popup: $('.code-line-menu'), on: 'click'});
+}