Attempt to re-enable autodiff in SwiftWasm presets (#4067)

Apparently, we've disabled autodiff when switching to builds with presets. Some SwiftWasm users actually would like to see it enabled.

Author: MaxDesiatov

utils/webassembly/build-presets.ini

@@ -8,6 +8,7 @@ llvm-targets-to-build=X86;AArch64;WebAssembly
 swift-darwin-supported-archs=%(HOST_ARCHITECTURE)s
 compiler-vendor=swiftwasm
 enable-experimental-concurrency=1
+enable-experimental-differentiable-programming=1
 
 [preset: webassembly-install]