On at least iOS 26 using a temporary window frame is unreliable. This
change tries to use an existing window for any non-standalone app. It
also updates the details on any changes, such as when the device
orientation changes.
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.
Deprecated methods returning a Display& in favour of new methods returning a Display* which return nullptr when running on a system with no connected displays.
