[SPARK-29504][WEBUI] Toggle full job description on click

### What changes were proposed in this pull request?
On clicking job description in jobs page, the description was not shown fully.
Add the function for the click event on description.

### Why are the changes needed?
when there is a long description of a job, it cannot be seen fully in the UI.
The feature was added in #24145
But it is missed after #25374

Before change:
![Screenshot from 2019-10-23 11-23-00](https://user-images.githubusercontent.com/51401130/67361914-827b0080-f587-11e9-9181-d49a6a836046.png)
After change: on Double click over decription
![Screenshot from 2019-10-23 11-20-02](https://user-images.githubusercontent.com/51401130/67361936-932b7680-f587-11e9-9e59-d290abed4b70.png)

### Does this PR introduce any user-facing change?

No

### How was this patch tested?
Manually test

Closes #26222 from PavithraRamachandran/jobs_description_tooltip.

Authored-by: Pavithra Ramachandran <pavi.rams@gmail.com>
Signed-off-by: Gengliang Wang <gengliang.wang@databricks.com>

Author: PavithraRamachandran

core/src/main/resources/org/apache/spark/ui/static/webui.js

@@ -87,4 +87,11 @@ $(function() {
   collapseTablePageLoad('collapse-aggregated-runningExecutions','aggregated-runningExecutions');
   collapseTablePageLoad('collapse-aggregated-completedExecutions','aggregated-completedExecutions');
   collapseTablePageLoad('collapse-aggregated-failedExecutions','aggregated-failedExecutions');
-});
+});
+
+$(function() {
+    // Show/hide full job description on click event.
+    $(".description-input").click(function() {
+        $(this).toggleClass("description-input-full");
+    });
+});