Adds a mechanism to notify the host that the plugin state needs saving,
using updateHostDisplay.

Also allows JUCE hosts to detect when a plugin needs its state saving
via the AudioProcessorListener.

This commit removes the various compiler-specific JUCE_DEPRECATED macros and replaces them with C++14's deprecated attribute. It also removes the JUCE_CATCH_DEPRECATED_CODE_MISUSE flag as we can rely on the override specifier catching usage of these old virtual methods, and tidies up the DOXYGEN preprocessor checks as they were inconsistent across the codebase.

Previously, updating the program or bypass parameter could cause an
out-of-bounds access into the parameter value cache. This is because
AudioProcessorParameter::getParameterIndex() was used to index into the
cache, but the parameter index could be negative for parameters that
had not been added to the AudioProcessor.

We now use the appropriate index in the cache for parameters that
have not been added to the AudioProcessor.

On some Linux distros, the audio settings dialog was opening with the
wrong size and position. The culprit seems to be the call to setSize()
which was called inside resized(). We now try to avoid calling setSize()
if we would do so inside a resized() call.

To use this feature, derive your AudioProcessor from
VST3ClientExtensions and override getPluginHasMainInput() to return
false. The main input bus will then be designated as an Aux bus, rather
than a Main bus.

This is mainly useful for synth plugins like vocoders, which may need a
sidechain audio input, but which should replace all audio on the channel
with the output of the synth, rather than mixing with the audio input.

See commit message of a1337a38 for more details

Ideally, we want to pass shortcut keys to the component to handle, and
only fall back to invoking a menu item if the component was unable to
handle the keyboard event, or if the action was triggered by
clicking/selecting an item in the menu itself. The old implementation
tried to work out whether the action was triggered by a shortcut by
checking the event's characters and modifiers. This method was
inaccurate, because some shortcuts (such as arrow keys) may add
unexpected numpad/function modifier flags.

We now try handling shortcut keys directly in the peer, and pass events
up to the superclass (which will forward them to the main menu) if the
event could not be handled.

This commit also adjusts some Objective-C method signatures to use the
correct string encoding for the BOOL type.

See BREAKING-CHANGES.txt for more details.

This function is required by the Steinberg VST3 validator from VST 3.7
onwards.

This fixes warnings that are emitted when building with the `-analyze`
flag enabled.

In cases where a VST3 plugin set a non-zero latency in its
prepareToPlay, and then set its latency to 0 later on, the host was not
notified about the latency change.