Reverts "Remove Fuchsia Mac SDK from DEPS" (flutter/engine#47791)

Reverts flutter/engine#47700
Initiated by: zanderso
This change reverts the following previous change:
Original Description:
Save infra capacity. Fuchsia commits 4 times a day, which can trigger a subsequent framework roll. Removing the Mac roller as it appears to be unused anymore.

Skia config is in https://skia-review.googlesource.com/c/skia-autoroll-internal-config/+/774657

DEPS

@@ -946,6 +946,16 @@ deps = {
 
   # Get the SDK from https://chrome-infra-packages.appspot.com/p/fuchsia/sdk/core at the 'latest' tag
   # Get the toolchain from https://chrome-infra-packages.appspot.com/p/fuchsia/clang at the 'goma' tag
+   'src/fuchsia/sdk/mac': {
+     'packages': [
+       {
+        'package': 'fuchsia/sdk/core/mac-amd64',
+        'version': 'CssR5Ci8l8Wn47xEJSW2TxuUVmr2DpJ1FX-kTlrIW9wC'
+       }
+     ],
+     'condition': 'host_os == "mac" and not download_fuchsia_sdk',
+     'dep_type': 'cipd',
+   },
    'src/fuchsia/sdk/linux': {
      'packages': [
        {