Exclude metainternal from C++ API snapshots

Summary:
Add */metainternal/* to ReactApple's exclude_patterns in the C++ API snapshot config. 
This directory may contain internal headers that are not part of the public React Native
C++ API surface.

Changelog: [Internal]

Differential Revision: D101879633

Author: lavenzg

scripts/cxx-api/config.yml

@@ -93,6 +93,7 @@ platforms:
       - "*/templates/*"
       - "*/components/progressbar/android/*"
       - "*/components/switch/androidswitch/*"
+      - "*/metainternal/*"
     exclude_symbols:
       - "Android"
       - "\\(Deprecated\\)"