Previously, spring-boot-docs used the java-base-plugin and then added
configuration on top. This has proven to be error prone, with the most
recent problem being that the tests were not being compiled and run.

This commit changes approach and applies the java plugin to the project
instead of the java-base plugin. Now, rather than adding the necessary
configuration to the base, the unwanted pieces of the java plugin's
configuration – specifically the jar and javadoc tasks – are disabled
instead. The DeployedPlugin has also been updated so that it does not
create a publication from the java component for projects that have a
disabled jar task.

Closes gh-22284