[SDK-2468] update unit test imports

[JagadeeshKaricherla-branch]

Summary

• fix lint errors
• update unit test imports to use src instead of library(in node_modules)
• abstract RNBranch to support new platforms apart from ios and Android in nativemodules

Motivation

Type Of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Testing Instructions

npm run test

cc @BranchMetrics/saas-sdk-devs for visibility.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.56%. Comparing base (492070c) to head (fb7205a).
Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #997       +/-   ##
===========================================
+ Coverage   44.24%   69.56%   +25.32%     
===========================================
  Files           4        3        -1     
  Lines         278      138      -140     
  Branches       88       47       -41     
===========================================
- Hits          123       96       -27     
+ Misses        116       23       -93     
+ Partials       39       19       -20     

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