Keep text boxes usable while typing

[Dronquavious]

Description

This updates Open Notes text editing so the keyboard no longer obscures newly created text boxes near the bottom of a page.

Changes

• Resize the editor area for the iOS keyboard.
• Reveal a newly created text box in a keyboard-safe part of the canvas.
• Preserve a trailing blank page when text is added to the final page, without jumping the viewport away from the active text box.
• Enable scrolling within multiline text boxes.
• Increase the default text-box height for more practical multi-line entry.

Why

Previously, creating or editing a text box near the bottom of a page could leave the cursor hidden behind the keyboard. This made longer typed notes impractical, especially around page boundaries.

Dependency

This PR uses the new Mobile Ink viewport APIs for revealing a page position and adding a page without automatically scrolling.