Draft: [Mac app] Upgrade deployment target to macOS 14 Sonoma

The Graphviz.app should be modernized to a recent macOS version to enable future development.

• Use current APIs. https://developer.apple.com/documentation/appkit/views_and_controls https://developer.apple.com/documentation/uniformtypeidentifiers https://developer.apple.com/documentation/webkit/wkwebview

• Define properties to enhance instance variable usage (e.g. .property syntax) https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html#//apple_ref/doc/uid/TP40011210-CH5-SW2

• Replace manual retain/release memory management with automatic reference counting. https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html#//apple_ref/doc/uid/TP40011210-CH5-SW3

• Use literal and subscript syntax with NSArray and NSDictionary objects. https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/FoundationTypesandCollections/FoundationTypesandCollections.html#//apple_ref/doc/uid/TP40011210-CH7-SW11

• Replace custom png/tiff toolbar icons with standard SF symbols. https://developer.apple.com/design/human-interface-guidelines/sf-symbols

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