The scaling machinery in the component peer was causing problems for
hosted plugin views. Scaling the plugin view size requires close
collaboration between the plugin and the host, and it's important for
the host to have exact control over the size of the plugin's view. The
removed code in the HWNDComponentPeer was modifying the sizes of
embedded plugin windows, which would often leave them at an incorrect
size.

The faulty behaviour was especially noticable with plugins that do not
support DPI-aware behaviour. I tested with the following plugins (VST2 +
VST3), which should all now display correctly in the AudioPluginHost,
and assume the correct size when opened on hi-res displays, or dragged
between displays with different scale factors:
- Plogue AlterEgo
- U-He Hive 2
- FabFilter Pro-C
- Native Instruments Supercharger
- Surge

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, BadMatch errors were seen when there were several modal
windows, each with a native titlebar. Moving a window would attempt to
restack the windows, which was not possible because the JUCE windows
were not siblings. We actually need to restack the top level windows,
i.e. the windows containing the server-side decorations.

Negative indices should count backwards from the last explicit
row/column number. If the resulting line number would appear before
the first explicit row/column, implicit grid lines should be added
before the first explicit row/column.

Previously, the following series of steps would leave the window at
full-size on Windows:

- Open a JUCE Window
- Maximise it
- Minimise it
- Click the maximise button

The expected behaviour is that the window should return to its initial
size and position, but instead the window still fills the screen.

This issue wasn't present on Ubuntu/Unity because minimising does not
invoke ComponentPeer::handleMovedOrResized on that platform. It was not
present on macOS because the system is responsible for restoring the
previous window size on that platform.

This fixes an issue where building with an old deployment target would
cause apps to display in "unsafe" screen areas.

This change stops menus from displaying under notches/cutouts on mobile
platforms.

This behaviour more closely mirrors the behaviour of other applications.

Previously, a touch on a component outside the Viewport would interrupt
and cancel a scroll gesture inside the Viewport.

Now, the Viewport will respond to all drag events from the input source
that started the drag, allowing the Viewport to be scrolled with one
input source while adjusting other controls with another input source.

The FontsDemo is useful for testing this behaviour, as it has two
Viewports on a single screen, along with some other controls.

Zenity and Kdialog only support opening either files or directories
during a single invocation.

This restores the behaviour of TreeViews with custom item components prior to ec990202