Add support for generated Java code with KSP

[zalewskise]

What has changed?

• Added support for Java generated code with KSP
• Renamed deshading to reshading to cover the case where plugins dependencies are clashing with kotlin compiler ones (proper solution would be: rules_kotlin should link the embeddable Kotlin compiler #624) and those need to be shaded.
• Added guava shading rules
• Added dagger code, generated with ksp plugin, to ksp sample project

Why it was changed?

• To be able to use Dagger’s KSP processor with kt_ksp_plugin

Fixes

• Support generating Java code with KSP #1074
• Issue with KSP picking up Kotlin Compiler classpath dependencies #1138

[Bencodes]

Doesn't this essentially mean that all targets that execute KSP will be forced to run a Java compilation action even if the underlying KSP plugin only produces Kotlin or class file outputs?

[zalewskise]

Great point, that's correct.

I'm thinking how we could avoid that and I'm not really sure how we could get the information if the plugin is generating java code or not, without getting this provided as one of kt_ksp_plugin parameters.
Could be something like

kt_ksp_plugin = rule(
    attrs = {
        "generates_java": attr.bool(
                doc = """Runs Java compilation action for plugin generating Java output"""",
                default = False,
        ),
       ...
    }
    ...
}    

What do you think about this approach? Or maybe there is some detail information that I'm missing, that could be used to determine if we could enforce/avoid running Java compilation action for certain KSP plugins? 👀

[zalewskise]

@Bencodes updated PR with the approach mentioned above