kcms/effects: Refactor UI code

Use ellipses instead of triple period

A real ellipsis character is better for accessibility, as screen readers will describe it appropriately.

Fix & modernize QML/JS code style

Key-value mapping is more convenient to use than iterating through array manually, and Map type is safer to use than plain old ECMAScript Object.

Set some sensible default (implicit) page size

so that kcmshell does not freak out with vertically collapsed window.

Set header label to WordWrap instead of eliding into nowhere

Set explicit spacing on layouts

Default value of 5 does not align with anything in KDE HIG.

Also a little bit of extra margin around the label looks better on top of a search field.

Set correct width expression for ListView delegates

Remove obsolete autoPlay property from Video component

It does not exist in Qt 6 anymore, and it's not very clear how to replace it.

Move footer actions to the page header

…to avoid the "two stacked rows of buttons" effect.

Changes "Get New" button text to avoid redundancy because title already contains the "Desktop Effects" string in it.

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And even after all those efforts, there's still key navigation to be fixed.

Also, ability to click on checked RadioButton to uncheck it is extremely unintuitive and breaks UX. I'd rather have sections per groups, and add None option for each. Maybe those groups could use some indentation or common rounded rectangle outline or whatever.