This commit switches UID hashing from md5 to a highway hash. It also
moves the salt value out of the file plugin - and makes it
installation-specific instead - it is moved to the global namespace.
There now are digest hash functions to make "static"
installation-specific hashes that are stable over workers available to
everyone; hashes can be 64, 128 or 256 bits in size.
Due to the fact that we switch the file hashing algorithm, all file
hashes change.
The underlyigng algorithm that is used for hashing is highwayhash-128,
which is significantly faster than md5.
The places that used md5 basically already used it as a digest
algorithm. Switching to a digest just means that the internal values
used to not change between runs - which is actually wanted in these
cases.
This commit also removes our special cmake subdirectory. We don't expose
highwayhash in headers anymore - so we can just treat it as an internal
implementation choice that is not directly exposed to plugins.
