Alice Mikhaylenko authored Feb 10, 2021 and Adrien Plazas committed Feb 11, 2021

We need to combine them with _HDY_EXTERN to handle exporting. Along the
way, align them with GDK, adding per-version deprecations, and drop the
duplicate macros we've never used. Drop hdy-deprecation-macros.h and merge
the 2 remaining macros into hdy-version.h as we need to declare them after
_HDY_EXTERN and it gets messy otherwise.