Better support for split packages.

- if you force an inclusion via 'inclusions=foo..*' then
  allow for everything in that package to be made reloadable
  regardless of it coming from jar or disk.
- when inclusion patterns don't match fall back on regular
  acceptance mechanisms (like package cache, etc) rather
  than just dismissing it.
- the results of decision making around making things
  reloadable are now enums/objects rather than plain booleans
  so that later we can do further analysis on those
  decisions.

Issue: https://github.com/grails/grails-core/issues/8817

testdata/jars/grailsplugins/build.sh

@@ -0,0 +1,4 @@
+mkdir -p grails/plugins
+cp ../../bin/grails/plugins/A.class ./grails/plugins/.
+jar -cvMf grailsplugins.jar grails/plugins/A.class
+