Improve size readability.
Preserve more space for swap devise names.
Prevent line overflow with long devise name.
Don't draw a bar when swap is not used at all.
Simplify and optimize code.
Change the label to end at end of 100%.
PR: 251655
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D27496

(cherry picked from commit 8d06c3e7a40831ac139d83b85b282206229b426f)