Refactor GetLockStatusData() by skipping unused backends and groups

Hi,

While reading the fast-path lock code, I noticed that GetLockStatusData()
checks all slots for every backend to gather fast-path lock data. However,
backends with PID=0 don't hold fast-path locks, right? If so, we can
improve efficiency by having GetLockStatusData() skip those backends early.

Additionally, when GetLockStatusData() checks a backend, it currently
goes through all the slots accross its groups. Each group has 16 slots,
so if a backend has 4 groups (this can change depending on max_locks_per_transaction),
that means checking 64 slots. Instead, we could refactor the function
to skip groups without registered fast-path locks, improving performance.
Since each set of 16 slots is packed into a uint32 variable (PGPROC->fpLockBits[i]),
it’s easy to check if a group has any fast-path locks.

I've attached a patch that implements these changes. This refactoring is
especially useful when max_connections and max_locks_per_transaction are
set high, as it reduces unnecessary checks across numerous slots.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION