The old API only allowed cancelling property "get" inquiries and
subscription updates. However, there are use-cases for cancelling other
requests too. e.g. switching between views in a JUCE app might mean that
it's no longer necessary to subscribe to a particular property.

Cancelling subscriptions ends up being quite involved. Different
handling is needed depending on whether the subscription is cancelled
before or after the responder replies to the initial request.
In addition, the responder may ask the initiator to retry a subscription
begin request.

The change does not affect plugin windows, which are created by the
host.

This change also avoids the AudioPluginHost leaving zombie child
processes behind.

The new class hold a list of ChildProcesses and periodically checks
their return value until they report termination. On Linux this check
is necessary to avoid leaving zombie processes behind.

This also adds missing KHRONOS_APIENTRY qualifications to the debug
callback type, which fixes potential crashes when running debug Win32
builds.

This fixes an edge case in which if listeners are both removed and added during a callback the added listener(s) may be called during the same iteration

- Prevent out of scope access of the listeners lock
- Allow clearing the listener list from a callback

viewDidDisappear may be called when a file is successfully selected.
presentationControllerDidDismiss is only called when the controller is
dismissed manually by the user, e.g. by tapping outside the sheet, or by
dragging it away.

Checking for sheet dismissal is necessary in iOS 15, but not in iOS 17.
In iOS 17, tapping outside the file chooser causes a callback to
documentPickerWasCancelled instead.

Even without this change the helpers would build correctly, but Xcode
would be unable to open them in the GUI and present them in red letters.

A path of "$(SRCROOT)/../../SomeFile.cpp" would lose the fake C:\ prefix
when the ellipses are collapsed, and trigger a non-absolute File
assertion.

This also reverts commit c456f67c3f.

A Timer will only be created for the analysis task when necessary. This
ensures that the ScopedJuceInitialiser_GUI member inside the
DocumentController is initialised before a Timer instance is even
created.

This makes the AU Client compatible with other classes also using the
ScopedJuceInitialiser_GUI, specifically the ARADocumentController.

Even if this focus change is being propagated up by a child Component.

Co-authored-by: Steve Lhomme <robux4@ycbcr.xyz>

- Subsequently drops support for Xcode 15.0 while allowing users who have already resolved Xcode 15.0 issues to continue building

While Google Drive seemingly isn't trying to access URI's that aren't an
exact match, without the presence of FLAG_GRANT_PREFIX_URI_PERMISSION,
sharing files with Google Drive will silently fail.