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/workbench/browser/modelComponents/image.component.ts

@@ -55,7 +55,7 @@ export default class ImageComponent extends ComponentWithIconBase implements ICo
 		if (this.iconPath) {
 			if (!this._iconClass) {
 				super.updateIcon();
-				DOM.addClasses(this.imageContainer.nativeElement, this._iconClass, 'icon');
+				DOM.addClasses(this.imageContainer.nativeElement, this._iconClass, 'codicon');
 			} else {
 				super.updateIcon();
 			}