Update as per review and increase the max height of the stack trace details

Author: zsxwing

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

@@ -120,6 +120,20 @@ pre {
   border: none;
 }
 
+.stacktrace-details {
+  max-height: 300px;
+  overflow-y: auto;
+  margin: 0;
+  transition: max-height 0.5s ease-out, padding 0.5s ease-out;
+}
+
+.stacktrace-details.collapsed {
+  max-height: 0;
+  padding-top: 0;
+  padding-bottom: 0;
+  border: none;
+}
+
 span.expand-additional-metrics {
   cursor: pointer;
 }

core/src/main/scala/org/apache/spark/ui/jobs/StagePage.scala

@@ -427,13 +427,15 @@ private[ui] class StagePage(parent: JobProgressTab) extends WebUIPage("stage") {
         error
       })
     val details = if (isMultiline) {
-      <span onclick="this.parentNode.querySelector('.stage-details').classList.toggle('collapsed')"
+      // scalastyle:off
+      <span onclick="this.parentNode.querySelector('.stacktrace-details').classList.toggle('collapsed')"
             class="expand-details">
         +details
       </span> ++
-        <div class="stage-details collapsed">
+        <div class="stacktrace-details collapsed">
           <pre>{error}</pre>
         </div>
+      // scalastyle:on
     } else {
       ""
     }

core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala

@@ -207,13 +207,15 @@ private[ui] class FailedStageTable(
         failureReason
       })
     val details = if (isMultiline) {
-    <span onclick="this.parentNode.querySelector('.stage-details').classList.toggle('collapsed')"
+    // scalastyle:off
+    <span onclick="this.parentNode.querySelector('.stacktrace-details').classList.toggle('collapsed')"
           class="expand-details">
       +details
     </span> ++
-      <div class="stage-details collapsed">
+      <div class="stacktrace-details collapsed">
         <pre>{failureReason}</pre>
       </div>
+    // scalastyle:on
     } else {
       ""
     }

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -1598,7 +1598,9 @@ private[spark] object Utils extends Logging {
 
   /** Return a nice string representation of the exception, including the stack trace. */
   def exceptionString(e: Throwable): String = {
-    if (e == null) ""
+    if (e == null) {
+      ""
+    }
     else {
       val stringWriter = new StringWriter()
       e.printStackTrace(new PrintWriter(stringWriter))
@@ -1609,6 +1611,7 @@ private[spark] object Utils extends Logging {
   /**
    * Return a nice string representation of the exception, including the stack trace.
    * It's only used for backward compatibility.
+   * Note: deprecated because it does not include the exception's cause.
    */
   @deprecated("Use exceptionString(Throwable) instead", "1.2.0")
   def exceptionString(