util-lib: split out allocation calls into alloc-util.[ch]

bus: sync with kdbus (ABI break)

core: rearrange code so that libsystemd/sd-bus/ does not include header files from core Stuff in src/shared or src/libsystemd should *never* include code from src/core or any of the tools, so don't do that here either. It's not OK!

core: Remove uninitialized warnings from bus-endpoint.c Gcc is spewing some warnings about uninitialized variables. Let's get rid of the noise.

hashmap: introduce hash_ops to make struct Hashmap smaller It is redundant to store 'hash' and 'compare' function pointers in struct Hashmap separately. The functions always comprise a pair. Store a single pointer to struct hash_ops instead. systemd keeps hundreds of hashmaps, so this saves a little bit of memory.

bus: add kdbus endpoint types Add types to describe endpoints and associated policy entries, and add a BusEndpoint instace to ExecContext.