414444 WebP: add libwebp based file format plugin

This MR incorporates a new file format plugin based on the official libwebp codec. It also brings in new import and export plugins that enable access to all the available configuration parameters in libwebp as of 1.20. (I have ifdef'd the most recent bits so it should compile with the latest LTS release.) This MR disables the existing qimageio plugin for the WebP MIME type.

BUG: 414444

CCMAIL: kimageshop@kde.org

Images

Import plugin:

Dimensions	Advanced

Export plugin:

General	Advanced (page 1)	Advanced (page 2)

Test Plan

Build Krita in as many systems as you can. Test import and export of WebP images.

I have personally checked this MR on Windows, Android and Linux AppImage.

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.