Add style for disabled anchor elements

[miguelatvaadin]

Description

The Anchor component implements the HasEnabled interface so it can be disabled, though the disabled attribute is not valid for a elements.

To emulate this feature the Anchor component will be updated so the href attribute is modified when disabled, but it must also have some visual effect so the user understands that the link is not clickable anymore.

Current behavior

Nothing happens when the Anchor element is disabled

Expected behavior

The visual appearance of the link changes when the Anchor component is disabled

References

vaadin/flow#10924

[rolfsmeds]

To be consistent with other components, the disabled link should use color: --lumo-disabled-text-color;

I do have one concern about this: If there are Vaadin applications out there that use anchors without href but with onclick handling instead, this change will make all those links look disabled, in which case this would be a breaking change (i.e. not backported to V14).

(@jouni do you have anything to comment here?)

[rolfsmeds]

The disabled state has already been fixed in the Flow component by removing the href attrib: vaadin/flow#11121

[rolfsmeds]

Also cursor should revert from pointer to default (if that does not already happen automatically when the href attrib is removed), and the hover effect (underline) suppressed.

[rolfsmeds]

Acceptance criteria:

• Anchors without href should use --lumo-disabled-text-color
• Only anchors with href should have hover style (underline)
• Anchors without href should use default cursor (rather than pointer)