Fix: Key actions not being handled

[AtlasAutocode]

Description

Fix: Page up and page down keys did not work.
Fix: Control + up/down or page-up/down failed to scroll document.
Fix: Up arrow cursor key did not work when font size > 24.
Fix: Outdent after indent text at start of document threw assert failure. Fault was incorrect return from editor RenderEditableContainerBox.childAtPosition when caret positioned at start of document.

Enter any text in empty document. Click the indent toolbar button. Click the outdent toolbar button. Program asserted 'The provided text position is not in the current node' because the container was empty.

Additional notes

Handling of keys on macOS needs review.

Checklist

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• [ X ] All existing and new tests are passing.
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Breaking Change

Does your PR require developers 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).
• [ X ] No, this is not a breaking change.