stdint-type updates

Created by: germasch

This are a couple of relatively small changes that aim to avoid the use of hardcoded type strings within adios2. For example, replace "unsigned long long int" by GetType<uint64_t>().

If this were done in all possible places, things shouldn't actually break if one were to rename "unsigned long long int" to "uint64_t" for clarity eventually, however, there are still more places that use hardcoded strings, and they're actually difficult to identify, since there also libraries (e.g. ffs) that also use strings for types, though not necessarily the same ones.

This patch changes behavior in one spot, where it now allows DataMan to use ZFP compression for int64_t, which was previously broken as it checked for "int64_t" and "long" type. Both have never been actual type strings, there used to be "long int", but that's also gone now.