Implement Into<CaptureError> for the default server function error type (#4205)

* implement Into<CaptureError> for the server function error type

* document the server function error type

* fix tests

packages/playwright-tests/default-features-disabled/src/main.rs

@@ -44,6 +44,6 @@ fn current_platform_features() -> Vec<String> {
 }
 
 #[server]
-async fn get_server_features() -> Result<Vec<String>, ServerFnError> {
+async fn get_server_features() -> ServerFnResult<Vec<String>> {
     Ok(current_platform_features())
 }