Add #include <format> to Bitmap.cpp

std::format is used in the implementation of the newly defined
getAshmemId method. But the include for it is not coming transitively on
all host platforms. Hence this explicitly adds it.

Flag: NONE only adding import
Bug: 369619160
Test: build libhwui on host
Change-Id: Iaf631b1f0c99bae897325d17c2eb28a1bb92fe66