Add external entity test

Issue: SPR-11376
Ensure all tests are executed in the Gradle build

Prior to this commit several test classes named "*Test" were not
recognized as tests by the Gradle build. This is due to the configured
inclusion of '**/*Tests.*' which follows Spring's naming convention for
test classes.

This commit addresses this issue by:

 - Renaming real test classes consistently to "*Tests".
 - Renaming internal test classes to "*TestCase".
 - Renaming @WebTest to @WebTestStereotype.
 - Disabling broken tests in AnnoDrivenStaticEntityMockingControlTest.
 - Modifying the Gradle build configuration so that classes ending in
   either "*Tests" or "*Test" are considered test classes.

Issue: SPR-11384