Rework post-processing comparison to de-duplicate code

<!-- markdown --> Users: With this change, several plugins that did not generate line comments now do. Developers: The `generic_postlog_compare` / `generic_pre_handler` / `generic_post_handler` functions have been deprecated and replaced with `module_postlog_compare` / `module_pre_handler` / `module_post_handler` functions. A new `root_postlog_compare` has been added that works similarly to `module_postlog_compare` for plug-ins that do not support the MODULE system. Using `root_postlog_compare` makes writing plug-ins for static linters significantly easier. See the associated APIs for more information.