Allow to format as HTML the title of input widgets (Bokeh 3.4)

[maximlt]

Bokeh 3.4.0 allows to format as HTML the title if its Input Widgets (see https://github.com/bokeh/bokeh/pull/13497). This is a feature I've wanted a few times, in particular when building a form to add that red asterisk people are used to that indicates a field is mandatory.

[philippjfr]

Yes indeed this is great, I think we'll do this at the same time as finally migrating from name to label or title to set the Widget.title.