Add option to show or not icons in menu

Add an option to override the native convention and let users decide if they want icons in menu.

Test Plan

• Choose a platform (Linux-Plasma/Linux-Gnome/Windows/Android/Mac).
• Check if icons are displayed or not in the menu with the current Krita version on this platform.
• Test the build from this branch for this platform, by default it should have the same behaviour as before.
• Go to "Configure Krita" -> "Miscellaneous" -> scroll to the bottom and find "Icons in menu" option. It should have "Default" selected in the combobox. Try to select "Yes", validate, and restart Krita: it should show the icons in the menu. Try to select "No", validate and restart Krita: it should not show the icons in the menu. Try to select "Default", validate and restart Krita: it should return to the initial default behaviour.
• Test on all platforms to confirm it works correctly everywhere.

For now I tested:

• In the linux docker build env, by default it doesn't show icons in the menu there, and all the options work correctly.
• The appimage on Plasma desktop, by default it shows icons in the menu, and all the options work correctly.
• Mac (Sequoia, tested by freyalupen), by default doesn't show icons in the menu, all the options work correctly.

Needs testing:

• Android
• Windows

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.
• Does the patch add a user-visible feature? If yes, is there a documentation MR ready for it at Krita Documentation Repository?

Reminder: the reviewer is responsible for merging the patch, this is to ensure at the least two people can build the patch. In case a patch breaks the build, both the author and the reviewer should be contacted to fix the build. If this is not possible, the commits shall be reverted, and a notification with the reasoning and any relevant logs shall be sent to the mailing list, kimageshop@kde.org.