Add `contentInsets` Parameter

[thecoolwinter]

Description

This PR adds a contentInsets parameter that lets users set an inset object for the editor. It also updates STTextView to be able to set the left inset correctly. When left nil the scroll view will use automatic insets.

This also doesn't override the overscroll option, but rather adds the overscroll after the insets are applied.

Related Issues

• Discord discussion
• STTextView commit

Screenshots

Adding top and left insets:

Adding left and bottom insets (scroller is also inset):

[Wouter01]

I'll give it a go tomorrow, but looks good!

[thecoolwinter]

~Ah shoot, don't merge it looks like a test is still failing. I'll fix it in a bit.~

Ready to review, just added some tests and fixed to pass the failing ones.