Previously, if SpringApplication.run failed due to the refresh of the
application context throwing an exception, the application context
would not be available during run failure handling. This meant that
null was passed to any SpringApplicationRunListeners, however the
javadoc for the finished method does not indicate that it is possible
for null to be passed in. In addition to the possibility of a
NullPointerException, a side-effect of this behaviour was that the
auto-configuration report was not produced when refresh fails, making
it useless as a tool for diagnosing refresh failures.

This commit updates SpringApplication to take a reference to the
application context as early as possible and, crucially, before it
has been refreshed. This means that refresh no longer has to succeed for
the context to be passed to any SpringApplicationRunListeners and that
they will now receive an inactive context, rather than a null context in
the event of a refresh failure.

Closes gh-5325