Increase the performance of some xml and html helpers

[alubbe]

Summary

We saw some performance issues in #742 that this PR tries to solve

Test plan

Both helpers are already tested, this just refactors their implementation.

[Siemienik]

Thank you for this PR, nice done
How big speedup you note after these changes?

[rogozind]

This is good. Regexp way of finding whether or not we need the escaping is even faster than the loop I suggested #742 .
In my test I got 25% increase in performance. I have 43K rows of data. It takes 20 secs to export. 50% used to go to create the spreadsheet and 50% used to go to write out the files. Out of these 10 secs 5 secs went to serialize various elements and 5 secs went to xmlEncode() calls. With the patch the xmlEncode dropped to near zero so export now takes 15secs.

Please accept this PR.