This change is designed to fix issues with views stealing focus and
being brought to the front when popup menus are dismissed.

To test this behaviour:
- Open two instances "a" and "b" of a plugin editor containing a
  ComboBox
- Click the ComboBox in editor "a", opening its PopupMenu
- Drag the titlebar of editor "b" to move it
- The PopupMenu should be dismissed, but editor "a" should *not* steal
  keyboard focus or be brought to the front

The issue was caused by DropShadower using the ComponentListener interface
to listen to its target Component's changes and creating shadow Components
only if the target was visible during the event callbacks. However it was
possible that during the events the target was not yet visible because one
of its parents was not visible. When the parent became visible it would not
trigger a callback for the observed child component.

The fix attaches a ComponentListener recursively to all parents starting
from the target and responds to each componentVisibilityChanged() event.

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.