[py][bidi]: add event handler support for browsing context (#16101)

* add event classes and tests

* add `get_event_names` classmethod and refactor event dict

* remove unused `BrowsingContextEvent` class

* refactor event handling to `_EventManager` class

* fix callback

* add tests for events

* add thread safety lock and tests

* break thread test into 4 tests

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Co-authored-by: Corey Goldberg <[email protected]>
Co-authored-by: Diego Molina <[email protected]>

Author: 3 people