Proposal: make utilities declared in Cleanup.h part of TS API

[Walt Karas]

See the PR https://github.com/apache/trafficserver/pull/10231 .  Cleanup.h
is currently available to plugins in include/tscpp/api .  The proposal is
to move it to include/ts .  The declarations currently in the
atscppapi namespace are moved to the tsapi::c_support namespace.  The
c_support sub-namespace is for declarations specifically designed to work
with declarations in tsapi::c .