injection_points: Add variant for injection_point_attach()

injection_points: Add variant for injection_point_attach()

This new function is able to take in input more data than the existing
injection_point_attach():
- A library name.
- A function name.
- Some private data.

This gives more flexibility for tests so as these would not need to
reinvent a wrapper for InjectionPointAttach() when attaching a callback
from a library other than "injection_points".  injection_point_detach()
can be used with both versions of injection_point_attach().

Author: Rahila Syed <rahilasyed.90@gmail.com>
Reviewed-by: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAH2L28sOG2b_TKkZU51dy+pWJtny1mqDmeFiFoUASGa0X0iiKQ@mail.gmail.com