Bugfix/291 iconborderwidth doesnt work

[codebude]

Summary
This PR fixes/implements the following bugs:

• The icon's border wasn't rendered (due to a former code removal, which made the parameter useless)
• The previous method for border rendering was refactored, to work without Region.Exclude(path) (which earlier led to problems on Linux environments)
• More testcases were written and existing ones improved

Test plan

Closing issues
Fixes #291