doc: Add a bit of documentation for Widget.OnDrawn
doc: Auto-fill docs for event handler using gen-handlerargs-docs tool

Compiling gen-handlerargs-docs.cs and running it on all assemblies
automatically fills in some documentation for event handlers.
doc: Remove obsolete gen-gtype-ctor-docs tool

It was used to document obsolete constructors with a GType parameter.
Those are gone now, so we don't need the tool anymore.
doc: Auto-fill docs for GType properties using gen-gtype-docs tool

The gen-gtype-docs automatically fills in the documentation for all
GType properties.
doc: Auto-fill docs for IntPtr constructors using gen-intptr-ctor-docs

The gen-intptr-ctor-docs automatically fills in the boilerplate
documentation for the IntPtr constructors.
doc: Auto-fill docs for virtual methods using gen-vm-docs tool
doc: Remove obsolete gen-finalize-docs.cs tool

It was used to automatically document the Finalize methods, which do not
exist anymore. We are now using the standard Dispose pattern, and the
Dispose methods only appear in a few places, so they can be documented
manually.
doc: Remove the GLib/Dbus.xml file, it's replaced by GLib/DBus.xml

The class was renamed some time ago, but the automatic update of the
docs didn't catch the removal of the old file.
release: Small adjustments to NEWS for 2.99.2