Replace isc_mem_*_aligned(..., alignment) with isc_mem_*x(..., flags)

Replace isc_mem_*_aligned(..., alignment) with isc_mem_*x(..., flags)

Previously, the isc_mem_get_aligned() and friends took alignment size as
one of the arguments.  Replace the specific function with more generic
extended variant that now accepts ISC_MEM_ALIGN(alignment) for aligned
allocations and ISC_MEM_ZERO for allocations that zeroes
the (re-)allocated memory before returning the pointer to the caller.