Escaped characters in XML or TeamCity reporters can be truncated incorrectly

[cschreib]

Some reporters (e.g. the XML reporter) require some characters to be escaped (e.g., & -> &). Because messages have a finite length and can be truncated, there were cases where the truncation happened in the middle of an escape sequence.

For example:

Hello this is me & my friend

being truncated to

Hello this is me &am...

The escaping logic needs to account for this, and avoid truncating in the wrong place.