Prevent whitespace from being added around highlights in regex search (#1710)

[blms]

In this PR

Per #1710:

• Prevent whitespace from being added around highlights in regex search, by not running clean_html on regex search

Notes

clean_html is not useful for regex search since the only html there will be <em> tags. We don't need to worry about malformed HTML there; and clean_html will try to add \n around <em> tags because it is a prettifier.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.92%. Comparing base (d15759c) to head (29e7bb6).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1718   +/-   ##
========================================
  Coverage    98.92%   98.92%           
========================================
  Files          245      245           
  Lines        15679    15683    +4     
========================================
+ Hits         15511    15515    +4     
  Misses         168      168