debug: show value in hover on the whole expression

fixes #4840

src/vs/workbench/parts/debug/browser/debugViewer.ts

@@ -70,6 +70,7 @@ export function renderVariable(tree: tree.ITree, variable: model.Variable, data:
 
 	if (variable.value) {
 		renderExpressionValue(variable, data.value, showChanged);
+		data.expression.title = variable.value;
 	} else {
 		data.value.textContent = '';
 		data.value.title = '';
@@ -658,6 +659,7 @@ export class WatchExpressionsRenderer implements tree.IRenderer {
 		data.name.textContent = `${watchExpression.name}:`;
 		if (watchExpression.value) {
 			renderExpressionValue(watchExpression, data.value, true);
+			data.expression.title = watchExpression.value;
 		}
 	}