[Yunq] POC for moving yunq parsing to a library.

lib/yunq/message_view.cpp

@@ -0,0 +1,19 @@
+#include "message_view.h"
+
+namespace yunq {
+
+template <>
+glcr::ErrorOr<uint64_t> MessageView::ReadField<uint64_t>(uint64_t field_index) {
+  return buffer_.At<uint64_t>(field_offset(field_index));
+}
+
+template <>
+glcr::ErrorOr<glcr::String> MessageView::ReadField<glcr::String>(
+    uint64_t field_index) {
+  ExtensionPointer ptr =
+      buffer_.At<ExtensionPointer>(field_offset(field_index));
+
+  return buffer_.StringAt(offset_ + ptr.offset, ptr.length);
+}
+
+}  // namespace yunq