`bevy_window`, `bevy_input_focus`, `custom_cursor` features moved to alternate feature collections

In Bevy 0.18, feature collections were introduced. The bevy_window, bevy_input_focus, & custom_cursor features were included in the default_app collection.

In Bevy 0.19, these have been moved from default_app:

This change was made because:

• the default_app collection is for core functionality that most apps will need. Scene definition for windowing is not usually required, and
• apps that don't use windowing (ex: command line tools, servers, etc) can compile fewer dependencies.

If you were relying on these being included in default_app, you can cherry-pick them into your Cargo.toml feature list:

# 0.18
bevy = { version = "0.18", default-features = false, features = [ "default_app" ] }

# 0.19
bevy = { version = "0.19", default-features = false, features = [
    "default_app",
    "bevy_window",
    "bevy_input_focus",
    "custom_cursor"
] }

If you already depend on a high-level profile (2d, 3d, ui), or a mid-level collection ending in '_render' or '_api', then you do not need to make any changes.

I've erred on the side of hopefully-longer-than-it-needs-to-be.