Add typings to UI Builder

[vostrik]

It will very helpful to add typings for UI Builder.
For 3 reasons:

1. For users (developers) — they get types for each handler type etc.
2. For maintainers — it will be more predictable to work with current code.
3. Also it unblocks the next step — @kaspersky/form-builder. Tool to build UI forms from typed code.