Add KCM.SettingHighlighter inside permissions page

Add KCM.SettingHighlighter inside permissions page

Now it can show which permissions' last loaded or effective values differ from their default values in metadata.

Note: Draft because it needs to be split into smaller MRs, and rebased on master once the MRs which it sits on top of are merged.

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other clean-ups in this branch:

Rename needsSaveChanged signals to settingsChanged

Just to match KConfigModule API.

Rename fields and methods without abbreviations

To make things clearer and easier to read.

(Note: this patch is specific to Plasma 6)

QML: Fix references to KcmUtils.ConfigModule object

This attached property doesn't work on arbitrary children items.

QML: Add some blank lines for readability

Add KCM.SettingHighlighter inside permissions page

Now it can show which permissions' last loaded or effective values differ from their default values in metadata.