[RNMobile] Improve editor's adaptability to device font size changes

[SiobhyB]

Description

Following support for Dynamic Type on iOS in #57339, there are more opportunities for improving how the editor adapts to font size changes made via a device's accessibility settings.

• Enforce a maximum and minimum display font size, to account for cases where users may set very small or large custom font sizes.
• Refactor so that RichText blocks adapt to updates to the Dynamic Type setting without a need to close and re-open the block editor.
• Review other areas of the editor for improvements.

Relevant notes/issues:

• Stepper cell label occasionally invisible when OS text scaled to the maximum #37995
• Accessibility: iOS Dynamic Type not being applied on the editor wordpress-mobile/gutenberg-mobile#4097 (comment)
• Improve the mobile editor's accessibility #54362
• [RNMobile] Words cut off when large font is enabled on Android #50057

Step-by-step reproduction instructions

• On iOS, navigate to the Accessibility section in the Settings app.
• Select Display & Text Size then toggle Larger Accessibility Sizes to on.
• Select a larger accessibility size.
• Open the WordPress app and navigate to the post or page editor.
• Navigate through some everyday writing flows.

Expected behaviour

For text to always be clear and legible, and not to collide or overflow UI.

Actual behaviour

There are some places where text is bigger than its container or where it can even be illegible, such as #37995.

Device information

• Device: iPhone XR
• WordPress app version: 23.8.1