Minor fixes for setup_native.sh

[catarial]

The current setup script does not allow only performing a setup for ios or android. This change would fix that by just requiring them to be explicitly set instead of trying to do them both if none are set.

The script now requires brew if the correct ruby installation is not found, regardless of OSX version.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 30.14%. Comparing base (4596d0c) to head (6dd71f1).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1180   +/-   ##
=======================================
  Coverage   30.14%   30.14%           
=======================================
  Files         118      118           
  Lines        5172     5172           
  Branches     1110     1158   +48     
=======================================
  Hits         1559     1559           
+ Misses       3611     3609    -2     
- Partials        2        4    +2     

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see 2 files with indirect coverage changes

[shankari]

I would suggest simplifying further and just always installing both iOS and android dependencies. We can also unify the two separate CI/CD builds into one - e.g. osx-native-install.