Fixed crash of reference pipes with the "--gui-only" option https://github.com/GrandOrgue/grandorgue/issues/2019

[oleg68]

Resolves: #2019

The reason of the crash was that GOReferencePipe internal structures were set up during the Initialise() call that was skipped with --gui-only.

This PR

• Introduces the new class GOReferencingObject that may refer to another objects that might be loaded from the ODF in any order.
• It's subclass should implement the OnResolvingReferences method where it should actually finds another objects from the model because they all have already loaded from the ODF.
• GOOrganModel::Load calls ResolveReferences of all GOReferencingObject instances as the last step of ODF loading
• GOReferencePipe is now a subclass of GOReferencingObject. GOReferencePipe::OnResolvingReferences now sets up it's internal structures instead of GOReferencePipe::Initialize().
• GOReferencePipe is not more a subclass of GOCachedObject because it needs to read neither any files nor the cache

[larspalo]

@oleg68 I can still reliably crash GO started with -g switch when I:

• open/load any sample set with a (synth) tremulant
• activate tremulant
• then de-activate the tremulant to cause the crash

I've confirmed that the steps above work for among others Burea Church (2023), Jeux d'Orgues 2, Norrfjärden, Pitea MHS and Orgue de Pibrac so the issue seems to be related to synthetic tremulants, as for instance Bygdsiljum with a wave tremulant doesn't cause a crash.

[oleg68]

@larspalo I fixed crash with a synth tremulant

[oleg68]

@rousseldenis Could you approve this PR?

[oleg68]

@rousseldenis Pourriez-vous approuver ce PR?