This commit ports multimaster to Postgres 14:
- removed tablespace-setup from mmts/Makefile
  (according to commit 6c788d9f6aadb41d76a72d56149268371a7895ee);
- add readOnlyTree flag to MtmProcessUtility()
  (according to commit 7c337b6b527b7052e6a751f966d5734c56f668b5);
- explicitly specify the hash function HASH_STRING
  (according to commit b3817f5f774663d55931dd4fab9c5a94a15ae7ab);
- refactor the use of EState
  (according to commit 1375422c7826a2bf387be29895e961614f69de4b);
- add 'include_out_arguments' to the function FuncnameGetCandidates()
  (caccording to commit e56bce5d43789cce95d099554ae9593ada92b3b7);
- use MyProc->xmin instead of MyPgXact->xmin in dmq.c
  (according to commit 73487a60fc1063ba4b5178b69aee4ee210c182c4);
- remove EE pooler support;
- use SearchNamedReplicationSlot() instead of ReplicationSlotAcquire()

1) Remove the target installcheck, because it is used during make
   installcheck-world.
2) Remove placeholder for the target check, because it looks like everything is
   already working..

Due to changing PROC->xmin type to pg_atomic_uint64.

…notests

For a build without assertions we get the following warning:

src/resolver.c: In function ‘handle_response’:
src/resolver.c:616:37: error: ‘gid’ may be used uninitialized in this function
[-Werror=maybe-uninitialized]