Register java plugin in Gradle plugins

[glefloch]

As discussed on zulip, Quarkus Gradle plugins can't work without the java plugin. A build could fail if plugin are not applied in a correct order. This applies the java plugin by default to make sure no error can happen.

/cc @grossws @gastaldi

[aloubyansky]

@glefloch should we adjust the templates that are used for project creation as part of this PR?

[gsmet]

I would keep it explicit in the generated project.

[aloubyansky]

I find this confusing. Why?

[glefloch]

I think this is a fallback to be more resilient to errors. Removing the java plugin, could lead to confusion if users need to configure java specific property ?

[aloubyansky]

I am not sure there is much value in this PR then.

[glefloch]

I tested it, the order of plugin does not create an issue. This just prevent error when user don't set set the java plugin.
This may have less interest indeed.

[grossws]

It's best practice to apply plugin if you depend on it and react to it with pluginManager.withPlugin if you have optional requirement. So I think the PR still has value.

Since plugin application is idempotent order in plugins with this patch wouldn't matter but will avoid confusion.

I tested it, the order of plugin does not create an issue

I had such issue in the past with older Gradle version (somewhere in 6.x) when plugin assumed that java is available when plugins { id("my-java-conventions") ; id("some.plugin.that.requires.java") }. See gradle/gradle/issues/15664