## Description

This PR adds a new channel to query the engine keyboard state.
See https://github.com/flutter/flutter/issues/87391#issuecomment-1228975571 for motivation. 

## Related Issue

Framework side implementation for https://github.com/flutter/flutter/issues/87391.

Once approved the framework will try to query the initial keyboard state from the engine. PRs will be needed on the engine side to answer the framework query.

## Tests

Adds 1 test.