Make it easier to find source of unexpected ability

[ceedubs]

I often encounter an error message like The expression in red needs the {IO} ability, but this location only has access to these abilities: {g5, Remote, Scope s8}. That's great (aside from some perplexing numbers appended to ability type parameters, but that's a separate issue).

But then when it shows me the offending code, it may be a block that is dozens of lines long. Is there a way that we could make it easier to spot where the offending code is?

This may be tricky, because there may be 1 or more nodes/lines requiring 1 or more unexpected abilities. Maybe the all could be highlighted? Even if it's easier to special-case 1 offending node/line, I think it would be pretty helpful.

Environment (please complete the following information):

• ucm --version 2d740dede