Previously, our Gradle plugin was not tested against Gradle 6.0,
a number of deprecation warnings were output when using the plugin
with Gradle 6, and some functionality related to the application
plugin did not work as expected.
This commit tests the plugin against Gradle 6. It also avoids calling
deprecated APIs. The plugin is compatibile against Gradle 4.10 where
the deprecated APIs' replacements are not available so reflection is
used to call the replcaements. Lastly, the way in which the base name
of the boot distribution that is created when the application plugin
is applied has been modified to ensure that it is effective when using
Gradle 6.
Closes gh-18663
Previously, Maven's default behaviour was relied up which resulted
in the artifact ID being appended to each URL as it was inherited.
This behaviour can only be disabled in Maven 3.6 and later, a version
that we cannot use due to an incompatibility with the Flatten Plugin.
This commit works around Maven's default behaviour by defining
properties for the SCM URL, connection, and developer connection and
then explicitly defining the settings in each pom using these
properties. The explicit definition of the properties in each pom
prevents them being inherited from the parent, thereby disabling the
unwanted appending of the artifact ID to the URL.
Fixes gh-18328
Apply checkstyle rule to ensure that private and package private
classes do not have unnecessary public methods. Test classes have
also been unified as much as possible to use default scoped
inner-classes.
Closes gh-7316