With the removal of all legacy code paths, obsconfig.h always exists and
the compile definition always gets set. As such, it's no longer
necessary to check for it.
As removing the definition itself could be seen as a breaking change,
this simply moves the definition to pc.in and cmake.in files for now to
preserve the value for plugins that might expect this to be set. We may
remove the definition entirely in a later release.
To emit frontend events early during OBS' initialization, the
disableSaving state variable needs to be "falsy" (as events will not be
emitted otherwise).
The code path taken for generating a new fallback scene collection
has disableSaving decremented to "enable" saving (and thus frontend
events) already, so it's just the code paths for existing collections
that need this workaround.
Emitting the scene changed and preview scene changed events when a
fallback scene collection has been created has side-effects when
OBS Studio is set to studio mode and can lead to potential crashes,
as the studio mode is still in an invalid state at this point.
