Set the minimum required Metal version for compatibility when running in an environment where it is not set to the latest version (contrary to what the documentation says)

Author: emezeske

filament/backend/src/metal/MetalShaderCompiler.mm

@@ -111,9 +111,14 @@ 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.
+                options.languageVersion = MTLLanguageVersion2_3;
 
                 assert_invariant(source[source.size() - 1] == '\0');
                 // the shader string is null terminated and the length includes the null character