bug#42028: [Feature Request] 27.0.91; Provide the ability dynamic modules to post events in emacs event loop

[Ivan Yonchovski]

This is needed for the cases when the module is listening for extenal
events and wants to call back emacs to process them. ATM this is kind of
possible by using signals on linux and using WM_INPUTLANGCHANGE as
described in https://nullprogram.com/blog/2017/02/14/ but this looks
more a hack for a missing feature.