Fix Apple frameworks alway building both modes (#12510)

### Summary

We currently always build both versions since the flags (--Release,
--Debug) append instead of override.

### Test plan


```
$ ./scripts/build_apple_frameworks.sh
→ MODES=("Release" "Debug")

$ ./scripts/build_apple_frameworks.sh --Release
→ MODES=("Release")

$ ./scripts/build_apple_frameworks.sh --Debug
→ MODES=("Debug")

$ ./scripts/build_apple_frameworks.sh --Release --Debug
→ MODES=("Release" "Debug")
```

cc @larryliu0820

Author: jathu

scripts/build_apple_frameworks.sh

@@ -7,7 +7,7 @@
 
 set -euxo pipefail
 
-MODES=("Release" "Debug")
+MODES=()
 PRESETS=("ios" "ios-simulator" "macos")
 # To support backwards compatibility, we want to retain the same output directory.
 PRESETS_RELATIVE_OUT_DIR=("ios" "simulator" "macos")
@@ -137,6 +137,11 @@ for arg in "$@"; do
   esac
 done
 
+# If no modes are specified, default to both Release and Debug
+if [[ ${#MODES[@]} -eq 0 ]]; then
+  MODES=("Release" "Debug")
+fi
+
 echo "Building libraries"
 
 rm -rf "${OUTPUT_DIR}"