Switch array_output_buffer.h to use QUICHE_EXPORT_PRIVATE for consistency with other targets in spdy/core.
Switch array_output_buffer.h to use QUICHE_EXPORT_PRIVATE for consistency with other targets in spdy/core.

This means it would be needed to be moved into a different target in Chromium.

PiperOrigin-RevId: 448526668

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