RPC simulateTransaction endpoint now returns program log output (#10432)

runtime/src/log_collector.rs

@@ -0,0 +1,16 @@
+use std::cell::RefCell;
+
+#[derive(Default)]
+pub struct LogCollector {
+    messages: RefCell<Vec<String>>,
+}
+
+impl LogCollector {
+    pub fn log(&self, message: &str) {
+        self.messages.borrow_mut().push(message.to_string())
+    }
+
+    pub fn output(self) -> Vec<String> {
+        self.messages.into_inner()
+    }
+}