Tabulator broken with HTMLTemplateFormatter

[mathrick]

ALL software version info

Panel 0.12.1

Description of expected behavior and the observed behavior

Recent change to support hierarchical tabulator breaks rendering with HTMLTemplateFormatter. Specifically, in ce68889, the changes to tabulator.ts peel off the HTML generated. I left a comment on #2624 on the exact lines, I don't know how to link to exact lines in an issue...

Complete, minimal, self-contained example code that reproduces the issue

pn.widgets.Tabulator(pd.DataFrame({'link': ['foo']}), 
                     formatters={'link': HTMLTemplateFormatter(
                         template='<a href="<%= value %>">Link</a>'
                     )})

Screenshots or screencasts of the bug in action

0.12.1:

0.12.0: