C# CaretReferenceHighlighter highlights incorrect offsets before it is being refreshed

[dgrunwald]

In a new C# console application, place the caret in the middle of the WriteLine identifier.
After a short time, the CaretReferenceHighlighter displays a light blue background highlight behind the word 'WriteLine'.

Now quickly press backspace several times. Note that for a short time, the end of the blue highlight stays at its old position, thus highlighting part of the string literal.
Similarly, when moving the caret, the blue highlight stays in its old place even when the caret is leaving the boundary of the current identifier.

Suggested fix:

1. Immediately remove the highlight whenever the document is changed
2. Immediately remove the highlight when the caret moves outside of the current identifier boundaries.