Fail the docs build on quick index config problems

[pvcraven]

Closes #2800

Problem

CI builds the docs with -W, so Sphinx's own warnings fail the build. doc/conf.py also runs util/update_quick_index.py to generate the API pages, and that script reported problems with print(), so they never failed anything. These included:

• "No members parsed for …", for a config entry that adds nothing to the docs
• "Failed to open …"
• "Exception processing …"
• "Unintelligible config data …", which also skips writing that page

A config entry for a module that doesn't exist already failed the build, because get_module_path raises.

Change

• The script now collects these problems and raises a RuntimeError at the end listing all of them. That stops the Sphinx build, and running the script on its own exits with an error.
• Removed the 7 config entries that caused the current "No members parsed" warnings:
  • arcade.sprite_list, arcade.texture, arcade.texture_atlas, arcade.anim and arcade.gui, whose __init__.py files only re-export names from submodules that are already listed
  • arcade.__main__, which has no classes or functions
  • arcade.types.numbers, which only defines the type alias AsFloat, and the parser only finds class and def
• AsFloat wasn't documented anywhere. A new "data" config option lists names to document with autodata. The types page uses it for arcade.types.numbers.AsFloat, which now appears on the page and in the quick index.
  • It's listed by its defining module because autodoc reads #: comments from there. Through the arcade.types re-export, it showed Python's built-in "Represent a PEP 604 union type" text.
  • Its comment now says what it is: "A float or an int. Arcade accepts either where it uses this type, and works with the value as a float."

The other type aliases in arcade.types (Point2, RGBA255, Velocity and so on) aren't documented either. They can be added to "data" later.

Testing

• The docs build with -W passes with no warnings, and the 7 "No members parsed" lines are gone.
• Adding arcade.types.numbers back to the config makes the build fail, with the problem listed in the error.
• I checked the rendered AsFloat entry on the types page.
• ruff and mypy pass.

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