Set the minimum required Metal version (#9425)

Author: emezeske

filament/backend/src/metal/MetalShaderCompiler.mm

@@ -111,9 +111,22 @@ bool isReady() const noexcept {
         id<MTLLibrary> library = nil;
         switch (program.getShaderLanguage()) {
             case ShaderLanguage::MSL: {
-                // By default, Metal uses the most recent language version.
                 MTLCompileOptions* options = [MTLCompileOptions new];
                 options.fastMathEnabled = YES;
+                // The docs for MTLCompileOptions say that Metal uses the most
+                // recent language version if it is not specified, but this is
+                // not always true: it is possible for the environment to be set
+                // up in a way where an older version is used by default. So we
+                // explicitly set the minimum version we require.
+                #if defined(FILAMENT_IOS)
+                    options.languageVersion = MTLLanguageVersion2_0;
+                #else
+                    if (@available(macOS 11.0, *)) {
+                        options.languageVersion = MTLLanguageVersion2_3;
+                    } else {
+                        options.languageVersion = MTLLanguageVersion2_2;
+                    }
+                #endif
 
                 assert_invariant(source[source.size() - 1] == '\0');
                 // the shader string is null terminated and the length includes the null character