Add QUICHE_EXPORT to the public inner class in binary_http_message.h
Add QUICHE_EXPORT to the public inner class in binary_http_message.h

Some of the methods of these inner classes were causing linking errors on Chrome Windows builds. See https://ci.chromium.org/ui/p/chromium/builders/try/win_chromium_compile_dbg_ng/1338006/overview for reference.

PiperOrigin-RevId: 485419068

google/quiche,google/quiche,google/quiche,google/quiche