Consider applying primary style to button with primary action

[web-devel]

See action's primary attribute.

Steps to reproduce

• set $cuba-highlight-primary-action:true;
• wire button to primary action

    <actions>
        <action id="primaryAction" primary="true"/>
    </actions>
    <layout>
        <button action="primaryAction" caption="Button with primary action"/>
    </layout>

Button is not highlighted.
Also consider to set $cuba-highlight-primary-action to true by default in Helium.

[glebfox]

• $cuba-highlight-primary-actionalready set to true by default in Helium, see https://github.com/cuba-platform/helium-theme/blob/master/modules/web/themes/helium/helium-defaults.scss#L168
• The problem described above isn't related to Helium. The Hover theme has the same problem:

[glebfox]

Related CUBA issue has been resolved: cuba-platform/cuba#2929.