[GREENFOOT-758] Flickering background while editing code that doesn't change scopes

See attached GIF, particularly in the early stages where the single if line is being edited. It would be good to eliminate this flickering.

Note: This example has a syntax error in it, although not curly bracket related. I see less flickering without the error. Will add more GIFs if I find more examples.

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Issue metadata

• Issue type: Task
• Priority: Medium