allow html tooltips via data-html-tooltip-title

html content supplied in data-tooltip-title shows up literally
in tooltips after the fix for CNVS-17449.

for tooltips with html content, this commit allows using
data-html-tooltip-title (on pre-sanitized HTML content!)

test plan:
 - ensure the module sequence footer tooltips,
   for each of
     (a) previous item in current module
     (b) previous module
     (c) next item in current module
     (d) next module
   all the following apply:
     (1) the tooltip is formatted properly (you don't see
         literal HTML code)
     (2) ... unless the module or module item's name *contains*
         HTML code. That is, ensure module and module item
         names are not XSS-able.

fixes CNVS-17637

Change-Id: I34a2e8df23448929efca27d7c3ac5ec4836db08c
Reviewed-on: https://gerrit.instructure.com/46213
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Mark Severson <markse@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
QA-Review: Sean Lewis <slewis@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>