Provide identical close/float tool options controls as in all other dockers

In point 7. of the UI feedback thread at https://krita-artists.org/t/krita-ui-papercuts/4704 an inconsistency in the tool options docker is pointed out: Unlike all other dockers, which generically feature a float and a close button on the top right, the tool options docker only has a float button.

I think there would be no negative implications from offering the close button also on this widget (please do correct me if I'm wrong of course), so this is a tiny MR to change that.

Test Plan

• Enable the "Tool options" docker if it isn't yet displayed
• Check if there are both a float and a close button on the top right of the docker widget
• Check if both do what they are meant to do
• Success

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.