Rework enabled/click handling in ListItem and ListItem-derived components

[blammit]

ListItem has an enabled state that is set by various ListItem-derived components.

This causes issues when gui-v2 needs to provide some default behaviour when an item is clicked, or for key navigation, when items cannot be disabled as that makes them non-focusable.

Investigate ways to rework ListItem and derived components to address this.

Issues that depend on this:

• Generic Solution to disabled ListItems' Toast raising strategy #1818
• "Setting locked for access level" is not shown when expected #1766
• Add read-only UI mode  #560
• Add keyboard navigation to gui-v2 #1030