Build script for self-contained Mac .app (#185)

* Add CMake settings to build universal binary and find SDL in app bundle

* Source frameworks from extern folder

* Add build script, info plist and big sur style icon

* Add example build workflow (app won't be signed)

* Use macOS 11 runner for better compatibility

* Use better name for the build script, move metadata to Platform/macOS/ folder

* Improve macOS build instructions

* Fix workflow syntax and use a more specific glob pattern too

* Add libs search paths to CMakeLists.txt instead of find files

* Use same /Libs folder as libs search path

* Make build-mac-app.sh not fail on repeated runs

* Make build-mac-app.sh executable

Platform/macOS/Info.plist

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>English</string>
+	<key>CFBundleExecutable</key>
+	<string>SpaceCadetPinball</string>
+	<key>CFBundleIconFile</key>
+	<string>SpaceCadetPinball.icns</string>
+	<key>CFBundleIdentifier</key>
+	<string>com.github.k4zmu2a.spacecadetpinball</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleLongVersionString</key>
+	<string></string>
+	<key>CFBundleName</key>
+	<string>SpaceCadetPinball</string>
+	<key>CFBundlePackageType</key>
+	<string>APPL</string>
+	<key>CFBundleShortVersionString</key>
+	<string>CHANGEME_SW_VERSION</string>
+	<key>CFBundleSignature</key>
+	<string>????</string>
+	<key>CFBundleSupportedPlatforms</key>
+	<array>
+		<string>MacOSX</string>
+	</array>
+	<key>CSResourcesFileMapped</key>
+	<true/>
+	<key>NSHighResolutionCapable</key>
+	<true/>
+</dict>
+</plist>