Prior to this change,
FrameworkServlet#configureAndRefreshWebApplicationContext called
#postProcessWebApplicationContext(wac) and #applyInitializers(wac)
prior to #refresh, but because servlet-based property source stubs were
not replaced until #refresh, any post-processing or initialization
routines could not benefit from accessing the Environment to retrieve
properties from the ServletContext or ServletConfig.
The workaround to this problem is detailed in SPR-9610 - the user simply
needed to call WebApplicationContextUtils#initServletPropertySources
manually within their ApplicationContextInitializer (or overridden
#postProcessWebApplicationContext method)
This commit ensures that
FrameworkServlet#configureAndRefreshWebApplicationContext calls
WebApplicationContextUtils#initServletPropertySources eagerly, prior to
invoking #postProcessWebApplicationContext and #applyInitializers.
Related Javadoc has also been updated throughout to clarify the behavior
of #initServletPropertySources, when it can be called and what the
effects are, etc.
Note also that a reproduction issue was added to demonstrate the problem
and verify its resolution [1].
[1]: https://github.com/SpringSource/spring-framework-issues/tree/master/SPR-9610
Issue: SPR-9610