Follow-up for the malloc_dispatch module added earlier in the stack.
The previous batch commits only touched files that existed when
cyclical_dep_h was written; malloc_dispatch.c was added later.
Pull the tcache-aware allocation routing helpers out of arena into a
layer that sits directly below the public malloc interface:
arena_malloc -> malloc_dispatch_malloc
arena_palloc -> malloc_dispatch_palloc
arena_ralloc -> malloc_dispatch_ralloc
arena_dalloc* -> malloc_dispatch_dalloc*
arena_sdalloc* -> malloc_dispatch_sdalloc*
arena_dalloc_promoted -> malloc_dispatch_dalloc_promoted
These helpers decide whether to route through tcache or fall through to
arena/large fast paths. They are now owned by malloc_dispatch_inlines.h
+ src/malloc_dispatch.c, and the only consumers are the public-front-end
wrappers in jemalloc_internal_inlines_c.h.
arena keeps a narrower arena_prof_demote() helper for the sampled
allocation demotion + redzone verification it used to perform inline.
arena_inlines_b.h no longer includes tcache_inlines.h -- the symbol
level arena <-> tcache cycle is gone (it's now in malloc_dispatch).
