System Variables Refactor: Eliminate `switch (opt_id)`

[ParadoxV5]

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• The Jira issue number for this PR is: TODO-5177

Description

~~Store method pointers instead of option IDs in Sys_var_rpl_filter and Sys_var_binlog_filter~~ Eh plans changed. I like mariadb-binlog filter objects – I wanna porting the design to mariadbd!

PR quality check

• [x] This is a new feature or a refactoring, and the PR is based against the main branch.
• ~~This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.~~
• [x] I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• [ ] For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.