Improve performance if there are no filters

Problem/Motivation

Config Split and Config Ignore are two of the most installed modules that depend on Config Filter. Both of them now have stable releases that use the core API which was added to replace Config Filter. When sites switch to these new versions they no longer depend on Config Filter. However, Drupal modules need to be uninstalled before they can be removed from the codebase. Config Filter can be uninstalled at the same time as upgrading the other module, but it would be good in any case to not do any useless and expensive copying of config if there is no need anyway.

Steps to reproduce

Install Config FIlter without any module adding filters.

Proposed resolution

Add a simple if statement and return early in the event subscribers.

Remaining tasks

Patch, commit, celebrate.

User interface changes

none

API changes

none

Data model changes

none