Improve performance when loading multiple editors on one page

Problem/Motivation

There are certain methods in CKEditor5PluginManager that run when loading each ckeditor instance on a page. The methods in question are getCKEditor5PluginConfig and getProvidedElements. Some static caching could be added to these methods to save some CPU cycles in case the editors have the same configuration.

Steps to reproduce

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Proposed resolution

Add static caching.

Remaining tasks

User interface changes

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Introduced terminology

API changes

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Data model changes

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Release notes snippet