Make it easier to opt out of bevy_audio

[janhohenheim]

Objective

• bevy_seedling is incompatible with bevy_audio
• all our profile features (3d, 2d, ui) enable the audio collection feature
• That means that a seedling user needs to do this to land at the current default:

[dependencies]
bevy = { version = "0.18.0", default-features = false, features = [
  # 2d
  "2d_bevy_render",
  "default_app",
  "picking",
  "scene",

  # 3d
  "3d_bevy_render",

  # ui
  "ui_api",
  "ui_bevy_render",

  # default_platform
  "android-game-activity",
  "bevy_gilrs",
  "bevy_winit",
  "default_font",
  "multi_threaded",
  "std",
  "sysinfo_plugin",
  "wayland",
  "webgl2",
  "x11",
] }

Solution

• Disable the audio collection features for all profile features and instead enable it by default
• The new seedling config now looks like this:

[dependencies]
bevy = { version = "0.18.0", default-features = false, features = [
  "2d",
  "3d",
  "ui",
] }

Testing

• None, CI should take care of this

[alice-i-cecile]

Summary of conversation on Discord about this work:

@cart: 2d / 3d as written were supposed to be "top level" collections that are "standalone". They each also pull in ui, scene, and audio, as those are all pieces of the "default 2d experience". I see the utility in reframing this (and thus forcing people to include the individual pieces they want manually), but we'd be losing the simplicity of single-feature profiles
@cart: If we're going to do that, I think we should consider what the lines are there. Ex: do we continue to include ui in 2d?
@alice-i-cecile: I think the top level features should be complementary and support common patterns. Splitting apart UI is also good
@cart: I think I agree. People disabling default features are doing so because they want control, and this is the level of granularity most of those people would be interested in. I just want to avoid getting to the point where building a "default 2D bevy app" requires knowing which 10 features to enable

[mnmaita]

I feel like this is a smart change. Even when "2d" is/was supposed to be something that enables a "full blown" 2d bevy app, it still requires to disable all default features and UI is still a separate thing so... And with audio it's been quite typical to use an external crate so far. Additionally, and semantically speaking, I'm not expecting a feature called "2d" to enable audio for me but that's just my point of view.

FWIW I had some ideas for the script that generates the cargo_features doc so I think I'll be working on some changes soon as this PR motivates me to improve and add more clarity to it.