Before this fix,

the perforance schema memory instrumentation
could cause runtime overhead when enabled.

The root cause is due to instruments with the following properties:
- the instrument flags are 0,
  defined as per thread and not global
- the instrumented memory is allocated / freed
  very often during execution
- the instrumented memory can be allocated by one thread
  and freed by a different thread.

Not having the global (PSI_FLAG_ONLY_GLOBAL_STAT) flag
indicates that the performance schema should maintain:
- per thread stats
- per account stats
- per user stats
- per host stats
as well as global statistics.

Frequent instrumentation, and memory transfer of ownership between threads,
causes a lot of overhead when maintaining the high/low water mark.

The affected code to maintain high/low water marks is:
- PFS_thread::carry_memory_stat_delta()
- PFS_account::carry_memory_stat_delta()
- PFS_user::carry_memory_stat_delta()
- PFS_host::carry_memory_stat_delta()

This fix requalifies many memory instruments as global,
with the flag PSI_FLAG_ONLY_GLOBAL_STAT.

This is a fix for both:

1) Correctness.

Instruments that keep track of a global resource,
for example "memory/sql/host_cache::hostname",
are by definition global.
Keeping per thread stats is meaningless.

2) Performances.

This avoids keeping track of high/low watermarks,
and reduce overhead.

Also, a minor bug was fixed in pfs_memory_claim_v1(),
which did not honor the PSI_FLAG_ONLY_GLOBAL_STAT flag.