fix(windows): release FFmpeg memory and capture native crashes (#1668)

ui/flutter/windows/runner/crash_handler.h

@@ -0,0 +1,12 @@
+#ifndef RUNNER_CRASH_HANDLER_H_
+#define RUNNER_CRASH_HANDLER_H_
+
+#include <windows.h>
+
+// Installs best-effort native diagnostics before Flutter or plugins start.
+void InstallCrashHandler();
+
+// Records the exception and continues normal Windows exception processing.
+LONG RecordNativeCrash(EXCEPTION_POINTERS* exception);
+
+#endif  // RUNNER_CRASH_HANDLER_H_