- macOS behaviour of setRealtime now matches other platforms

MR feedback

- added unit tests
- best performance timers used for each platform
- fixed an issue in which timer callbacks could drift

This commit adds fixes for generating unique hardware IDs on Windows. The SMBIOS is parsed to generate a unique ID based on hardware factors of the local machine.

The issue affected projects not depending on juce_audio_devices.

Previously, JUCE_ANDROID_REALTIME_THREAD_AVAILABLE sometimes remained
unset, even though JUCE_USE_ANDROID_OBOE was set to its default value.
This is because in this case, JUCE_USE_ANDROID_OBOE is only defined in
juce_audio_basics.h, so it is not visible when compiling juce_core.cpp.

This is a breaking change - see BREAKING-CHANGES.txt

The current minimum-supported Xcode (10.1) includes the macOS 10.14.1
SDK, so APIs from macOS 10.14 will always be available.

The current minimum-supported Xcode (10.1) includes the macOS 10.14.1
SDK, so APIs from macOS 10.13 will always be available.

The current minimum-supported Xcode (10.1) includes the macOS 10.14.1
SDK, so APIs from macOS 10.12 will always be available.

The current minimum-supported Xcode (10.1) includes the iOS 12.1 SDK, so
APIs from iOS 12 will always be available.

The current minimum-supported Xcode (10.1) includes the iOS 12.1 SDK, so
APIs from iOS 10 will always be available.

The current minimum-supported Xcode (10.1) includes the iOS 12.1 SDK, so
APIs from iOS 10 will always be available.

Previously, input streams created by AndroidDocument instances did not
implement setPosition, so they were not useful for reading some file
formats, such as WAV.

Due to limitations of the Java InputStream interface, seeking backwards
in a stream requires creating a whole new stream and seeking from the
beginning, so it could be quite slow.