Field Widget Actions show in the "Add New Action" unavailable tools

Problem/Motivation

Field Widget Actions plugin has a method isAvailable, it is currently widely used in AI Automators. The main requirement for a plugin to be available in case of an automator, this automator should exist for that entity type and field. When displaying the dropdown list the availability is not checked, only the base field type/field widget checks are done.

This leads to a confusion when a plugin is available in the list, but it can't be really added, because when "Add" button is clicked, the isAvailable conditions is checked.

Steps to reproduce

1. Install ai_automators module. Do not create any automators.
2. Install field_widget_actions module.
3. Create a content type with taxonomy reference field, or go to Manage form display of existing content type/entity type with such field.
4. Make sure the widget for taxonomy reference is "Autocomplete (Tags style)" (this step is not required, just make sure that there is a plugin that corresponds to your widget type).
5. In the dropdown list you will see the "AI Automators -> Automator Taxonomy"
6. Try to add this action
7. Observe that action is not added and no error message is displayed.

Proposed resolution

Either add the error message in case the action was not added. Maybe for this some changes will be needed to actually display the reason why the action can't be added, more verbose mode in case isAvailable returns FALSE. Or another solution do not display in the list the plugins that are not available.

Remaining tasks

Decide on the approach and implement.