Policy Editor: Improve UX when user tries to add # comments

[GammaSQ]

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Qubes OS release

4.2

Brief summary

When trying to disable a rule with a target (replacing allow with deny), commenting the target (putting a # in front of it) gives the error: "Invalid parameters for action Deny: ['#target=anothervm']"

Expected behavior

Comments at the end of lines are supported.

Or, if this is undesirable for psychological reasons (I could imagine "one line should always be a valid policy"), the error should be highly visible, maybe directly address the invalidity of comments.

Actual behavior

Currently, the comment is tinted blue like other valid comments and Errors are displayed in the exact same style as the "Policy file syntax" Text-wall in the right panel. (in fact it looks even smaller)
The Save Changes buttons look like they are disabled for no reason.

I would not have guessed the Error-message is an important blocker until I carefully searched for reasons why the "save changes" button was disabled. some red color or warning-icons would be helpful.