SortMenu: clean up

list of patches:

Fix whitespace

SortMenu: Bump QML import versions

SortMenu: Add QQC2 import alias

This is commonly used in KDE software for disambiguation and readability.

SortMenu: Rename root component id to root

This is easier to read, and is a common practice to name your top-level component like just root or control.

SortMenu: Use qualified properties access as appropriate

Not needed in top-level methods and expressions, preferred everywhere else.

SortMenu: Explicitly require index property in Repeater delegate

Explicitness is better than relying on magical context properties.

SortMenu: Change sortOrder property's type to int, add type hint in comment

Other var properties are arrays, and can't be better typed in Qt5/QML.