This allows real-time threads to join an audio workgroup on Apple platforms.

This fixes a warning when running xcodebuild directly

Enabling the hardened runtime also enables library validation, which
means that the manifest generator may not be able to load the built
plugin if the generator runs before the signing step.

The manifest generator tools should not be distributed/archived, so
disabling the hardened runtime for these targets is appropriate.

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

This reverts commit 82377a787a.

Reintegrates changes from cf9fc84669

- Created a new detail namespace
- Moved shared module implementation details into the detail namespace
- Split dependencies so source files only rely on details in the detail namespace
- Removed all code from the juce_gui_basics.cpp file