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/parts/notebook/browser/cellViews/media/output.css

@@ -469,7 +469,7 @@ plotly-output .plotly-wrapper {
 	overflow-y: hidden;
 }
 
-output-component .grid-panel .action-label.icon {
+output-component .grid-panel .action-label.codicon {
 	min-width: 16px;
 	margin-right: 6px;
 	margin-bottom: 6px;

src/sql/workbench/parts/notebook/browser/outputs/markdownOutput.component.html

@@ -1,5 +1,5 @@
 <div style="overflow: hidden; width: 100%; height: 100%; display: flex; flex-flow: row">
-	<div class="icon in-progress" *ngIf="loading === true"></div>
+	<div class="codicon in-progress" *ngIf="loading === true"></div>
 	<div #output link-handler [isTrusted]="isTrusted" [notebookUri]="notebookUri" class="notebook-preview" style="flex: 1 1 auto">
 	</div>
 </div>