Support for Rounded Corners Background Color Style

[aibobrov]

Currently inline code fragment (``) is rendered using build-in SwiftUI attribute backgroundColor.
To be more accurate with GitHub theme inline code fragment should be rendered with rounded-corner-background.

It can be done with SwiftUI's new TextRenderer api (useful article)

[antonjazz]

Yes - and it would look much nicer to have a small amount of padding around the text in the shaded code shape.