If TemplateStyles installed, then enable it in the Module namespace
by default. This change is analogous to I96d9601ff80c2d3eb052c01.
Since both extensions use the ContentHandlerDefaultModelFor hook, Scribunto
will check if the sanitized-css model has already been set, and if so, not
override it. If the page is in NS_MODULE, it will set the content model to
Scribunto, but allow further hooks to override it, in which case it is
expected that TemplateStyles would set it to sanitized-css.
Bug: T200914
Depends-On: I2fa9b822ee39bcc5f95a293c8c4aad4d53ede30a
Change-Id: I7a9b445accde35e4a5e7d13100c646f211d21afe
