Fix errors due to icon to codicon rename in VSCode (#7837)

Found numerous errors where icons weren't rendering correctly.
- Anything that's an action must have CSS using "codicon" not "icon"
since VSCode sets the "codicon" class automatically.
This affected Agent view in particular, but also:
  - acounts view
  - new tab view in dashboard
 - many more
- Anything referencing the common-icons.css icons needed updating.
This hid help tooltip text in FormContainer UI for example.
- Finally I tried to convert all references from icon -> codicon,
even when the CSS was technically correct. This was done
for maintainability reasons - from now on always add codicon.

Fixes #7827

src/sql/base/browser/ui/taskbar/taskbar.ts

@@ -64,7 +64,7 @@ export class Taskbar {
 	 */
 	public static createTaskbarSpinner(): HTMLElement {
 		let spinnerContainer = document.createElement('div');
-		spinnerContainer.className = 'taskbar-progress icon in-progress ';
+		spinnerContainer.className = 'taskbar-progress codicon in-progress ';
 		spinnerContainer.style.visibility = 'hidden';
 		return spinnerContainer;
 	}