Improve macOS bundling (#1067)

* Improve macOS bundling
* Bundle libs for macOS CI
* Add MACOS_BUILD_DMG CMake option and make the CI upload the DMG so we don't lose executable permissions.
* Manually copy plugins if macdeployqt doesn't
* Ad-hoc codesign the app

tools/msys-dist.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+if [[ ! -x melonDS.exe ]]; then
+	echo "Run this script from the directory you built melonDS."
+	exit 1
+fi
+
+mkdir -p dist
+
+for lib in $(ldd melonDS.exe | grep mingw | sed "s/.*=> //" | sed "s/(.*)//"); do
+	cp "${lib}" dist
+done
+
+cp melonDS.exe dist
+windeployqt dist