trigger 'affixed.bs.affix' instead of 'affixed'

Original is triggering `affixed` not `affixed.bs.affix`, only `.on('affixed.bs.affix', ...)` also catch `affixed` event.

Closes #13998.
no need to create $.Event

`trigger()` can handle string argument
Merge pull request #13998 from steelywing/patch-1