Improve display of long app captions and name/caption padding

Summary:

• Reduce padding between app name and caption to connect them a bit better
• Allow app caption string to have up to two lines when it's long and the window is narrow

Test Plan:
Tested in NDE Neon.

Blender, before:

Blender, after:

LibreOffice Writer, before:

LibreOffice Writer, after:

GIMP, before:

GIMP, after:

Reviewers: apol, Discover Software Store, VDG

Reviewed By: apol, Discover Software Store

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D10023