Adjacent strings expression in lists should be error, warning, or otherwise noticeable

[DartBot]

This issue was originally filed by [email protected]

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I have often run into bugs of the following form:

["a", "b", "c", "d" "e", "f"] // Can you notice a missing comma?

Without a close inspection, you easily conclude that the list declaration is correct.

A proposal:
Make it noticeable in the editor (color, etc.) when adjacent strings expression is used.
Considering making it an error or warning to use adjacent strings expression in list literals (and argument lists?).

[madsager]

Added Area-Language, Triaged labels.

[gbracha]

Reassigning to the editor,in case they can make it a hint. I was never a fan of the adjacent string concatenation idea, but we certainly aren't going to oscillate back and forth and make it illegal or a warning.

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Removed Area-Language label.
Added Area-Editor label.

[sethladd]

Adding some sort of visual indication seems reasonable. I, too, have been bit by this.

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Removed Type-Defect, Area-Editor labels.
Added Type-Enhancement, Area-Analyzer labels.

[bwilkerson]

Removed Priority-Unassigned label.
Added Priority-Medium, Analyzer-Hint labels.

[srawlins]

Dup of #4979