Issue sidebar and misc css fixes (#15524)

- Replace remaining font icons with SVG in issue sidebar
- Rework issue due date display
- Realign avatar in timeline
- Fix font size in repo search and code explore
- Consolidate active button styles
- Fix loading form on arc-green
- Align time tracker buttons vertically

Fixes: https://github.com/go-gitea/gitea/issues/15896

web_src/less/_editor.less

@@ -55,6 +55,10 @@
   background: var(--color-active);
 }
 
+.editor-statusbar {
+  color: var(--color-text-light);
+}
+
 .editor-loading {
   padding: 1rem;
   text-align: center;