Fix missing steps and fields in "report an error" in log module. (#838)

Missing steps common to the regular console events:

- Creating the `timestamp` field.
- Creating `body` from `entry`.

Also, the `stack` value was created in its own step, but was not
listed in the list of fields creating the specific
`log.JavascriptLogEntry` production.

index.bs

@@ -10992,15 +10992,20 @@ ignore>line number</var>, <var ignore>column number</var>, |message| and
 
 1. Let |settings| be |script|'s [=script/settings object=].
 
+1. Let |timestamp| be a [=time value=] representing the current date and time in UTC.
+
 1. Let |stack| be the [=stack trace for an exception=] with the exception
    corresponding to the error being reported.
 
 1. Let |source| be the result of [=get the source=] given [=current Realm Record=].
 
 1. Let |entry| be a [=/map=] matching the <code>log.JavascriptLogEntry</code> production,
    with <code>level</code> set to "<code>error</code>", <code>text</code> set to
-   |message|, <code>source</code> set to |source|, and the <code>timestamp</code>
-   field set to |timestamp|.
+   |message|, <code>source</code> set to |source|, <code>timestamp</code>
+   set to |timestamp|, and the <code>stackTrace</code> field set to |stack|.
+
+1. Let |body| be a [=/map=] matching the <code>log.EntryAdded</code> production, with
+     the <code>params</code> field set to |entry|.
 
 1. Let |related navigables| be the result of [=get related navigables=] given |settings|.