log system info on startup (bevyengine#5454)

# Objective

- We already log the adapter info on startup when bevy_render is present. It would be nice to have more info about the system to be able to ask users to submit it in bug reports

## Solution

- Use the `sysinfo` crate to get all the information
  - I made sure it _only_ gets the required informations to avoid unnecessary system request
- Add a system that logs this on startup
  - This system is currently in `bevy_diagnostics` because I didn't really know where to put it.

Here's an example log from my system:
```log
INFO bevy_diagnostic: SystemInformation { os: "Windows 10 Pro", kernel: "19044", cpu: "AMD Ryzen 7 5800X 8-Core Processor", core_count: "8", memory: "34282242 KB" }
```
---

## Changelog

- Added a new default log when starting a bevy app that logs the system information

crates/bevy_diagnostic/src/lib.rs

@@ -2,6 +2,7 @@ mod diagnostic;
 mod entity_count_diagnostics_plugin;
 mod frame_time_diagnostics_plugin;
 mod log_diagnostics_plugin;
+use bevy_log::info;
 pub use diagnostic::*;
 pub use entity_count_diagnostics_plugin::EntityCountDiagnosticsPlugin;
 pub use frame_time_diagnostics_plugin::FrameTimeDiagnosticsPlugin;
@@ -15,10 +16,62 @@ pub struct DiagnosticsPlugin;
 
 impl Plugin for DiagnosticsPlugin {
     fn build(&self, app: &mut App) {
-        app.init_resource::<Diagnostics>();
+        app.init_resource::<Diagnostics>()
+            .add_startup_system(log_system_info);
     }
 }
 
 /// The width which diagnostic names will be printed as
 /// Plugin names should not be longer than this value
 pub const MAX_DIAGNOSTIC_NAME_WIDTH: usize = 32;
+
+#[derive(Debug)]
+// This is required because the Debug trait doesn't detect it's used when it's only used in a print :(
+#[allow(dead_code)]
+struct SystemInfo {
+    os: String,
+    kernel: String,
+    cpu: String,
+    core_count: String,
+    memory: String,
+}
+
+const BYTES_TO_GIB: f64 = 1.0 / 1024.0 / 1024.0 / 1024.0;
+
+fn log_system_info() {
+    // NOTE: sysinfo fails to compile when using bevy dynamic or on iOS and does nothing on wasm
+    #[cfg(all(
+        any(
+            target_os = "linux",
+            target_os = "windows",
+            target_os = "android",
+            target_os = "macos"
+        ),
+        not(feature = "bevy_dynamic_plugin")
+    ))]
+    {
+        use sysinfo::{CpuExt, SystemExt};
+
+        let mut sys = sysinfo::System::new();
+        sys.refresh_cpu();
+        sys.refresh_memory();
+
+        let info = SystemInfo {
+            os: sys
+                .long_os_version()
+                .unwrap_or_else(|| String::from("not available")),
+            kernel: sys
+                .kernel_version()
+                .unwrap_or_else(|| String::from("not available")),
+            cpu: sys.global_cpu_info().brand().trim().to_string(),
+            core_count: sys
+                .physical_core_count()
+                .map(|x| x.to_string())
+                .unwrap_or_else(|| String::from("not available")),
+            // Convert from Bytes to GibiBytes since it's probably what people expect most of the time
+            memory: format!("{:.1} GiB", sys.total_memory() as f64 * BYTES_TO_GIB),
+        };
+
+        info!("{:?}", info);
+    }
+}