Fix map key in PreparerThread pending streams.

mPendingStreams in PrepareThread was a map
[max stream buffers -> Camera3Streaminterface].

This would cause two streams with the same max buffers to be added
to the map only once which is unintended.

Changed mPendingStreams from
std::unordered_map<int, Camera3StreamInterface>  to
std::list<std::tuple<int,Camera3StreamInterface>>

Bug: 259735869

Test: NativeCameraDeviceTest.java#testCameraDevicePrepareSurface

Change-Id: I501b9d2fab4705bf24a2ec8b628803392a36f44b
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>