Switch versioning scheme to be the same as GLib and Flatpak

For stable releases, this gives us the ability to make bugfix-only point
releases such as 2.24.1 if we want to, and distinguish between them
programmatically. For example, this ability could have been useful after
2.0.16 to fix Xwayland regressions, and after 2.0.18 to fix event loop
regressions.

For development releases, this gives us the ability to make multiple
prereleases during the same feature cycle, and distinguish between them
programmatically. For example, this would have been useful during 2.0.22
development, which went through three prereleases before reaching the
final release.

Signed-off-by: Simon McVittie <smcv@collabora.com>

Xcode/SDL/Info-Framework.plist

@@ -19,10 +19,10 @@
 	<key>CFBundlePackageType</key>
 	<string>FMWK</string>
 	<key>CFBundleShortVersionString</key>
-	<string>2.0.23</string>
+	<string>2.23.0</string>
 	<key>CFBundleSignature</key>
 	<string>SDLX</string>
 	<key>CFBundleVersion</key>
-	<string>2.0.23</string>
+	<string>2.23.0</string>
 </dict>
 </plist>