Run clang-tidy modernize-use-override to remove all the redundant
virtual keywords from overridden methods, and add some missing
overrides.
Another benefit is that this has also added the overrides
on destructors, which will cause a build failure if a base
class is missing a virtual destructor.
* add In annotation
* remove struct forward declarations
* fix members initialization list in header
* merge removal code for function bodies and constructor definition
The original name was not representative for the scope of the class
and misleading at best.
The class manages actions for a given layer and it's not a single action
like the former name suggested.
There is a typedef introduced to keep it in the API until we can remove
it with QGIS 3.
Rationale:
- there was a lot of large objects passed by value, so potentially
there's a speed bump from this
- even for implicitly shared classes like QString/QList there's still
a (small) cost for copying the objects when there's no reason to
- it's the right thing to do!
