[EAK-357] Add the ability to add extra widgets without adding redundant class fields

[liubou-masiuk]

As a toolkit user
I want to have the ability to add extra dialog widgets without adding unnecessary class fields
So that there are fewer linter warnings and less redundant code

The API is currently under discussion.

❔ what kind of widgets should have such functionality? @Heading, @Button, @Alert for sure, what about other widgets?

❕ need to make sure that annotations like @Property, @Attribute, @DependsOn, custom handlers(maybe)

❔ how will the order of fields be specified?