https://jira.mariadb.org/browse/MDEV-26221
my_sys DYNAMIC_ARRAY and DYNAMIC_STRING inconsistancy

The DYNAMIC_STRING uses size_t for sizes, but DYNAMIC_ARRAY used uint.
This patch adjusts DYNAMIC_ARRAY to use size_t like DYNAMIC_STRING.

As the MY_DIR member number_of_files is copied from a DYNAMIC_ARRAY,
this is changed to be size_t.

As MY_TMPDIR members 'cur' and 'max' are copied from a DYNAMIC_ARRAY,
these are also changed to be size_t.

The lists of plugins and stored procedures use DYNAMIC_ARRAY,
but their APIs assume a size of 'uint'; these are unchanged.

Note, the fix for "MDEV-23328 Server hang due to Galera lock conflict resolution"
was null-merged. 10.4 version of the fix is coming up separately

1. only call calc_sum_of_all_status() if a global
   SHOW_xxx_STATUS variable is to be returned
2. only lock LOCK_status when copying global_status_var,
   but not when iterating all threads

The functional changes of commit 5836191c8f0658d5d75484766fdcc3d838b0a5c1
(MDEV-21168) are omitted due to MDEV-742 having addressed the issue.