Add Controls Icons to Font and Match Current Inputs
## Problem
Currently each game either uses text or custom graphics to spell out what the controls are, generally by mentioning the keyboard keys to press. This works as long as you are on a PC and have the same keyboard layout. but quickly becomes wrong if you play through retroarch, mobile, or just don't have a standard layout. The current alternative is to use WASM4's naming standard (1, 2, Arrow Keys, etc.), but this is confusing to people who haven't memorized WASM4's buttons and their mappings.

## Proposal
We should add icons to the font that indicate each control (as in #195), and create a system that can swap these icons out with more appropriate icons at runtime. For web/desktop, this means that people can remap the controls to their preference and get correct instructions on what to press. On touch screens we can either add names (1, 2) to the on screen buttons and put this in the icons. In the retroarch builds we can use the retropad as our basis. For implementations of WASM4 on constrained devices this system can be ignored entirely and the icons hard coded into the engine.