`TreeStructureChanged` marked as `true` when whitespace is added to a page with `TagHelper`s

[NTaylorMullen]

The Razor editor uses the TreeStructureChanged property to determine if a full-parse should occur. Today, if there's a TagHelper on a page hitting Enter results in its value being set to true. This winds up causing unneeded parsing of the document.

[Eilon]

So this is a perf issue?

[NTaylorMullen]

On the editor side yes. I didn't want to mark it as perf because for Razor it's more of a bug that alleviates the editors perf issue 😄

[NTaylorMullen]

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