Add cancellation on CustomEditor.save

For #91702

src/vs/vscode.proposed.d.ts

@@ -1227,9 +1227,11 @@ declare module 'vscode' {
 		/**
 		 * Save the resource.
 		 *
+		 * @param cancellation Token that signals the save is no longer required (for example, if another save was triggered).
+		 *
 		 * @return Thenable signaling that the save has completed.
 		 */
-		save(): Thenable<void>;
+		save(cancellation: CancellationToken): Thenable<void>;
 
 		/**
 		 * Save the existing resource at a new path.

src/vs/workbench/api/browser/mainThreadWebview.ts

@@ -625,7 +625,7 @@ class MainThreadCustomEditorModel extends Disposable implements ICustomEditorMod
 		if (!this._editable) {
 			return false;
 		}
-		await this._proxy.$onSave(this.resource, this.viewType);
+		await createCancelablePromise(token => this._proxy.$onSave(this.resource, this.viewType, token));
 		this.setDirty(false);
 		return true;
 	}

src/vs/workbench/api/common/extHost.protocol.ts

@@ -618,7 +618,7 @@ export interface ExtHostWebviewsShape {
 	$undo(resource: UriComponents, viewType: string): void;
 	$redo(resource: UriComponents, viewType: string): void;
 	$revert(resource: UriComponents, viewType: string): void;
-	$onSave(resource: UriComponents, viewType: string): Promise<void>;
+	$onSave(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void>;
 	$onSaveAs(resource: UriComponents, viewType: string, targetResource: UriComponents): Promise<void>;
 
 	$backup(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void>;

src/vs/workbench/api/common/extHostWebview.ts

@@ -350,8 +350,8 @@ class CustomDocument extends Disposable implements vscode.CustomDocument {
 		this.updateState();
 	}
 
-	/** @internal*/ _save() {
-		return this.getEditingCapability().save();
+	/** @internal*/ _save(cancellation: CancellationToken) {
+		return this.getEditingCapability().save(cancellation);
 	}
 
 	/** @internal*/ _saveAs(target: vscode.Uri) {
@@ -714,9 +714,9 @@ export class ExtHostWebviews implements ExtHostWebviewsShape {
 		document._revert();
 	}
 
-	async $onSave(resourceComponents: UriComponents, viewType: string): Promise<void> {
+	async $onSave(resourceComponents: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void> {
 		const document = this.getCustomDocument(viewType, resourceComponents);
-		document._save();
+		document._save(cancellation);
 	}
 
 	async $onSaveAs(resourceComponents: UriComponents, viewType: string, targetResource: UriComponents): Promise<void> {