[Spike] Font sizes

## Description
There appear to be major disparities in how different font sizes are rendered in .NET MAUI vs. Xamarin.Forms.

## TODO
Investigate all named and numbered Font sizes, across all platforms, and between Xamarin.Forms and .NET MAUI, to ensure a reasonable pattern of consistency

Create a list documenting all the sizes for documentation

Compare named and numbered font sizes across Xamarin.Forms and .NET MAUI on all platforms, recording the observed values and identifying major disparities. The issue names no files, tests, or entry points, so begin by locating the font-size definitions and platform-specific rendering behavior. Done means a documented list of sizes and a clear consistency assessment.

Written by the indexing model from the issue text.