Mac: Update the bundled MoltenVK to 1.4.2, raise the macOS minimum to 12.0

1.4.0 never applied dynamic blend constants, so fixed-color blends lost
their constant factor on Vulkan (the Enemy panel in Tales of Phantasia
went dark, also Block Transfer effects). MoltenVK 1.4.2 requires macOS 12.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CMakeLists.txt

@@ -510,8 +510,8 @@ if(NOT MSVC)
 	if(IOS)
 		set(CMAKE_OSX_DEPLOYMENT_TARGET "12.0")
 	elseif(APPLE AND NOT CMAKE_CROSSCOMPILING)
-		# The oldest libc++ in current Xcode supports ("The selected platform is no longer supported" below).
-		set(CMAKE_OSX_DEPLOYMENT_TARGET "11.0")
+		# The bundled MoltenVK (ext/vulkan/macOS) needs 12.0.
+		set(CMAKE_OSX_DEPLOYMENT_TARGET "12.0")
 		add_compile_options("$<$<COMPILE_LANGUAGE:CXX>:-stdlib=libc++>" -U__STRICT_ANSI__)
 		set(CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LIBRARY "libc++")
 	elseif(NOT ANDROID)