Code-gen buildable projects by default

[joeduffy]

Unless I'm mistaken, Java code-gen doesn't produce buildable projects by default. You need to specify the BuildFiles option, as in:

LanguageMap: map[string]any{
    ...
    "java": javaGen.PackageInfo{
        BuildFiles: "gradle",
    },
    ...
}

This results in a build.gradle file in the root of the project. If I skip this, all that gets created is the code, with no project or build file. I expected a pom.xml in the root directly as the default.

This was not super easy to discover especially with the pulumi package gen-sdk command since it won't let you pass these options at the command line.

I love that I can opt into Gradle with the above option if that's what I prefer, but my naive assumption would have been that we generate Maven by default. It's likely we'd want an opt-out option for users who want full control.

As it stands, I believe the current behavior means Java is the only language SDK whose code-gen is not buildable by default.