https://perconadev.atlassian.net/browse/PS-9148

- Added caching of mysql.masking_dictionaries table content.
- Implemented masking_dictionaries_flush() UDF which flushes data
  from the masking dictionaries table to the memory cache.

https://perconadev.atlassian.net/browse/PS-9148

The masking_functions.masking_database system variable for the
masking_functions component specifies database used for data
masking dictionaries.

https://perconadev.atlassian.net/browse/PS-9148

- Added component_masking.dictionaries_flush_interval_seconds system
  variable.
- Added actual flusher thread. It periodically rereads content of
  dictionary table and updates in-memory cache.

https://perconadev.atlassian.net/browse/PS-9148

Introduced 'dictionary' and 'bookshelf' classes for storing terms on
per-dictionary level.
Reworked 'query_cache' to utilize these two new classes.

https://perconadev.atlassian.net/browse/PS-9148

Introduced 'component_sys_variable_service_tuple' class for groupping comonent
system variable registration services (supposed to be used with
'primitive_singleton' class template).

'query_cache' now expects 'query_builder' and 'flusher_interval_seconds' as its
constructor's parameters.

Eliminates custom MySQL types (like 'ulonglong') and its includes (like
'my_inttypes.h') from the publicly facing headers.

'query_cache' is now explicitly initialized / deinitialized in the component's
'init()'' / 'deinit()'' functions via 'primitive_singleton' interface.

'query_cache' helper thread-related methods made private.

https://perconadev.atlassian.net/browse/PS-9148

As std::string_view::data() is not guaranteed to be null-terminated, it is
not safe to use it in old c-functions accepting 'const char *'.
Some constants converted to arrays of char 'const char buffer[]{"value"}'.

https://perconadev.atlassian.net/browse/PS-9148

'command_service_tuple' struct extended with one more member - 'field_info'
service.

Reworked 'query_cache' class: instead of loading terms from the database in
constructor, this operation is now performed in first attempt to access one
of the dictionary methods ('contains()' / 'get_random()' / 'remove()' /
'insert()'). This is done in order to overcome a limitation that does not
allow 'mysql_command_query' service to be used from inside the componment
initialization function.
Fixed problem with 'm_dict_cache' shared pointer updated concurrently from
different threads.
Exceptions thrown from the cache loading function no longer escape the
flusher thread.

De-coupled 'sql_context' and 'bookshelf' classes: 'sql_context' now accepts a
generic insertion callback that can be used to populate any type of containers.

'component_masking_functions.dictionary_operations' MTR test case extended with
additional checks for flushed / unflushed dictionary cache.

https://perconadev.atlassian.net/browse/PS-9148

Both 'dictionary' and 'bookshelf' classes no longer include their own
'std::shared_mutex' to protect data. Instead, we now have a single
'std::shared_mutex' at the 'query_cache' level.

The return value of the 'get_random()' method in both 'dictionary' and
'bookshelf' classes changed from 'optional_string' to 'std::string_view'. Empty
(default constructed) 'std::string_view' is used as an indicator of an
unsuccessful operation.
'get_random()' method in the 'query_cache' class still returns a string by
value to avoid race conditions.

Changed the behaviour of the 'sql_context::execute_dml()' method - it now
throws when SQL errors (like "no table found", etc.) occur.