Configurable class scanning when running from IDE

[mshabarov]

Describe your motivation

Configurable class scanning for Maven showed a good performance gain in prepare-frontend and build-frontend maven goals for building frontend. Whereas this is enough for production builds, it would be more handy in development to have the same feature when running / debugging from IDE, where maven plugin does not come onto stage, so that you can exclude what not need a scanning and have faster restarts and reloads.

Describe the solution you'd like

Having similar configuration properties that one can setup in application.properties for example:

vaadin.frontend.scanner.includes=com.example:my-addon,com.foo:bar
vaadin.frontend.scanner.excludes=com.example:backend
vaadin.frontend.scanner.includeOutputDirectory=false

Describe alternatives you've considered

This feature does a similar exclusion that vaadin.(allowed|blocked)-packages properties do in Spring add-on, so maybe we could re-use them or enhance a bit. Alternative is to just port (allowed|blocked)-packages parameter to non-Spring configurations if the same optimised scanning can be achieved with (allowed|blocked)-packages.

Additional context

There are some complications like:

• In dev mode we do not have a centralised piece like the FrontendDependencies classes
• There are several ServletContainerInitializers that handles found classes
• Spring add-on adds its own logics for vaadin.(allowed|blocked)-packages
• To expand a bit the logic around the Vaadin package.properties file to allow add-ons auto-detection.