Fix for keyboard jumping when switching focus from a TextField

[oligazar]

Description

When user switches focus from a TextField to QuillEditor keyboards "jumps". This happens, because _handleFocusChanged is called in a postFrameCallback if the state is dirty. So there's time to start hiding keyboard animation and the show it again.

This fixes it by requesting keyboard prior to calling _handleFocusChanged in a postFrameCallback.

Related Issues

Replace this paragraph with a list of issues related to this PR from the issue database. Indicate, which of these issues are resolved or fixed by this PR.

e.g.

• Fix Keyboard jumps when QuillEditor gains focus #1779
• *Related Prevent operations on stale editor state #1256 *

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the plugin version in pubspec.yaml files.
• All existing and new tests are passing.
• I have run the commands in ./scripts/before_push.sh and it all passed successfully

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.