[Fuchsia] Disable C-ARES resolver

C-ARES does not work on Fuchsia, and is causing DNS solution failures.
We are disabling C-ARES so that we fall back to the native resolver.

Issue: #25446

include/grpc/impl/codegen/port_platform.h

@@ -366,6 +366,7 @@
 #define GPR_ARCH_32 1
 #endif /* _LP64 */
 #elif defined(__Fuchsia__)
+#define GRPC_ARES 0
 #define GPR_FUCHSIA 1
 #define GPR_ARCH_64 1
 #define GPR_PLATFORM_STRING "fuchsia"