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.

The AAX SDK already checks for truncated IDs internally. If any ID is
truncated, details will be written to Pro Tools' log file (you may need
to enable logging first). Search for "AAX_ASSERT" in the log to find
triggered assertions.

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

This patch fixes an issue where calling `updateHostDisplay` with no
argument would have no effect.

This patch fixes an issue where calling `updateHostDisplay` with no
argument would have no effect.

Previously, if `AudioProcessorGraph::prepareToPlay` was called twice,
interspersed with calls to `setProcessingPrecision`, the graph would
consider the nodes 'prepared' on the second call, and wouldn't
re-prepare the inner nodes with the new precision setting.

    graph.setProcessingPrecision (juce::AudioProcessor::singlePrecision);
    graph.prepareToPlay (44100, 512);

    graph.setProcessingPrecision (juce::AudioProcessor::doublePrecision);
    graph.prepareToPlay (44100, 512); // this wouldn't update the nodes

Now, we always explicitly unprepare all nodes at the beginning of
prepareToPlay, so that they'll always receive the newest settings.

We also build this into the AudioPluginHost, as a convenient way to
check the midi outputs of plugins and devices.