Clean up draw_commands in areas potentially helpful for #2065

[pushfoo]

Changes

TL;DR: Try to improve readability ahead of camera refactor research & prototyping

Why?

TL;DR: Help @DragonMoffon & @DigiDuncan when working on cameras

1. Good news: I finished investigating our pyglet 2.1 Vec* issues much sooner than expected

• Looks like a bad merge + overzealous __eq__ check
• Need to follow-up with pyglet team
• Probably easily fixed with a pyglet==2.1dev3 release

2. Rects would help make cameras less brittle (see Initial cleanup of arcade.types #2065's follow-up / description)

• We have a repeated root cause of projection / bounding box bugs due to lack of nice rect abstractions
• The bugs due to this keep piling up as I perform intensive code review (newest is that up vector breaks properties)

3. Digi & Dragon's feasibility checks / "census" for rect abstraction may have glossed over function internals
   • Signatures inspected
   • Unsure about implementations, especially on hard to read code
4. The comments here a requests for further refactoring
5. Improving readability lowers friction for delivering those refactors in future PRs

Where?

TL;DR: Function bodies where things help draw rects or might use quads

In draw_commands.py, wherever things look like:

1. Shared drawing helpers
2. Directly rectangle related
3. Appear to contain quad-like structures (see draw_polygon_outline)

How?

TL;DR: Make the code understandable before even attempting to fix how fast it runs

1. Replace long ugly inlined logic with Color's:
   1. from_iterable classmethod
   2. normalized property
2. Try to fail fast by putting these higher up:
   1. Window & context fetch
   2. Storing local refs to the context's shader & buffer singletons
   3. Color.from_iterable(color) validation
   4. Allocations of new array.arrays
3. General readability improvements, including:
   1. Split nested one-liner expressions
   2. Store re-used quantities in local variables
   3. Add comments
   4. Remove redundant conversions such as the tuple in (array.array('B', tuple(generator))
   5. * unpacking positional point arguments instead of indexing

[pushfoo]

1. I ran python -m arcade.examples.drawing_primitives and nothing seems off
2. If needed, I run do pixel comparison between branch outputs later