Extract action for publications compiling

[caendesilva]

Since these page types have dynamic source files, their compiling logic is a bit more complex than other pages. This refactor PR moves these to a dedicated action, and adds an experimental base action that adds a static call method to provide syntactic sugar for invokable classes.

The short snippet shows the call method alternative. Both lines to the exact same thing.

return (new PublicationPageCompiler($this))->__invoke();

return PublicationPageCompiler::call($this);