Add no_std support to bevy_window (#17031)

# Objective

- Contributes to #15460

## Solution

- Added the following features:
  - `std` (default)
  - `bevy_reflect` (default)
  - `libm`

## Testing

- CI

## Notes

- `bevy_reflect` was previously always enabled, which isn't how most
other crates handle reflection. I've brought this in line with how most
crates gate `bevy_reflect`. This is where the majority of the changes
come from in this PR.

---------

Co-authored-by: Alice Cecile <[email protected]>

crates/bevy_window/Cargo.toml

@@ -9,24 +9,69 @@ license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]
-serialize = ["serde", "smol_str/serde", "bevy_ecs/serialize"]
+default = ["std", "bevy_reflect"]
+
+# Functionality
+
+## Adds runtime reflection support using `bevy_reflect`.
+bevy_reflect = [
+  "dep:bevy_reflect",
+  "bevy_app/bevy_reflect",
+  "bevy_ecs/bevy_reflect",
+  "bevy_input/bevy_reflect",
+]
+
+## Adds serialization support through `serde`.
+serialize = [
+  "serde",
+  "smol_str/serde",
+  "bevy_ecs/serialize",
+  "bevy_input/serialize",
+]
+
+# Platform Compatibility
+
+## Allows access to the `std` crate. Enabling this feature will prevent compilation
+## on `no_std` targets, but provides access to certain additional features on
+## supported platforms.
+std = [
+  "bevy_app/std",
+  "bevy_ecs/std",
+  "bevy_input/std",
+  "bevy_math/std",
+  "bevy_reflect?/std",
+  "serde?/std",
+  "raw-window-handle/std",
+]
+
+## Uses the `libm` maths library instead of the one provided in `std` and `core`.
+libm = ["bevy_math/libm"]
 
 [dependencies]
 # bevy
-bevy_app = { path = "../bevy_app", version = "0.15.0-dev" }
-bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev" }
-bevy_input = { path = "../bevy_input", version = "0.15.0-dev" }
-bevy_math = { path = "../bevy_math", version = "0.15.0-dev" }
-bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", features = [
+bevy_app = { path = "../bevy_app", version = "0.15.0-dev", default-features = false }
+bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev", default-features = false }
+bevy_input = { path = "../bevy_input", version = "0.15.0-dev", default-features = false }
+bevy_math = { path = "../bevy_math", version = "0.15.0-dev", default-features = false }
+bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", default-features = false, features = [
   "glam",
   "smol_str",
-] }
-bevy_utils = { path = "../bevy_utils", version = "0.15.0-dev" }
+], optional = true }
+bevy_utils = { path = "../bevy_utils", version = "0.15.0-dev", default-features = false }
 
 # other
-serde = { version = "1.0", features = ["derive"], optional = true }
-raw-window-handle = "0.6"
-smol_str = "0.2"
+serde = { version = "1.0", features = [
+  "alloc",
+  "derive",
+], default-features = false, optional = true }
+raw-window-handle = { version = "0.6", features = [
+  "alloc",
+], default-features = false }
+smol_str = { version = "0.2", default-features = false }
+log = { version = "0.4", default-features = false }
+spin = { version = "0.9.8", default-features = false, features = [
+  "spin_mutex",
+] }
 
 [target.'cfg(target_os = "android")'.dependencies]
 android-activity = "0.6"