Prevent Windows console window for yaaknode and yaakprotoc

Add new_xplatform_command() helper in yaak-common that creates a
tokio::process::Command with CREATE_NO_WINDOW flag set on Windows.

Also converts git commands to async for consistency.

crates/yaak-common/src/command.rs

@@ -0,0 +1,16 @@
+use std::ffi::OsStr;
+
+#[cfg(target_os = "windows")]
+const CREATE_NO_WINDOW: u32 = 0x0800_0000;
+
+/// Creates a new `tokio::process::Command` that won't spawn a console window on Windows.
+pub fn new_xplatform_command<S: AsRef<OsStr>>(program: S) -> tokio::process::Command {
+    #[allow(unused_mut)]
+    let mut cmd = tokio::process::Command::new(program);
+    #[cfg(target_os = "windows")]
+    {
+        use std::os::windows::process::CommandExt;
+        cmd.creation_flags(CREATE_NO_WINDOW);
+    }
+    cmd
+}