Adds support for adding preFilter on a per-action basis, to assist in
plugin development. If action.preFilter function is passed, and returns
true/false, the action is shown/hidden. If no preFilter is specified,
then the action will be passed through the detail view's standard filter.
Example:
testAction: {
label: 'Test Action',
...
preFilter: function(args) {
return false; // Action will be hidden
},
...
}
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