XmlCommentHelper.GetText Performance issues

[ninedan]

There are a few performance issues in GetText implementation:

1. It's recreating regular expression every time, rather costly, especially on .Net framework.
2. Even using regular expression itself is not idea. The reason is that even single white space is a match when no replacement is actually needed, but it will still be performed.
3. Usage of reused StringBuilder is not optimal, because new string is always allocated.

Suggestion: do not use regular expression, aim for not a single allocation when no change is needed.

[ninedan]

Current implementation:

[ninedan]

Pull request: #3651

[bjornhellander]

Can this be closed now?