Provide an API to find a Java class for component with a given tag

[mshabarov]

Describe your motivation

Vaadin Copilot needs a way to find which Java component corresponds to e.g. vaadin-horizontal-layout. Vaadin Flow to provide an API to give this information, i.e. give a Class<? extends Component> for the given String tag.

Describe the solution you'd like

To include scanning for AtTag in the scanner that finds AtJsModule at a build time and produce a map <String, Class<? extends Component>>, which is available with a public API.

Additional context

Limited to only DEV mode, not needed for PROD.

Targets Vaadin 24.5.