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:
{F5669092}

Blender, after:
{F5669093}

LibreOffice Writer, before:
{F5669094}

LibreOffice Writer, after:
{F5669095}

GIMP, before:
{F5669096}

GIMP, after:
{F5669098}

Reviewers: apol, #discover_software_store, #vdg

Reviewed By: apol, #discover_software_store

Subscribers: plasma-devel

Tags: #plasma

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