Futher optimisation opportunity from bug 119286 comment 14

Quote:
"We repeatedly revalidate the paragraph signature. Since we're making changes to individual words/letters, this is effectively O(n^2). A smarter thing to do would be to only do this validation after the replace operation."

This "is tricky because it uses the UNO API to inspect the document, while the rest of the code is using the internal raw API"

Perf can be tested like so:
1. Open attachment 144181 [details]
2. Disable the automatic spell checking if enabled
3. In the Search for field put "." (a single period)
4. In the Replace with field put "x"
5. Make sure Whole words only is unchecked
6. Click Other Options to expand the dialog, and make sure Regular expressions is checked
7. Click Replace All