[GREENFOOT-441] Code wrapping breaks the line in some awkward places

HangingFlowPane currently breaks the line between any two arbitrary nodes. But certain nodes should have restrictions: no breaking between a string literal text field and its surrounding quotes, no breaking a line before a comma, and probably a few others. We should improve HFP to allow don't-break-before-here annotations on particular nodes.

Issue metadata

Issue type: Bug
Priority: Medium
Fix versions: 3.0.1