Increase code coverage to 90% (resolves #42)

[emdobrin]

Description

• Adds new tests to increase code coverage to 90%
• Added few helper functions for test body size reduction
• Removes internal usages of VisitorID objects and VisitorIDSerializer, uses DataReader and base types, and adds more tests on serializing custom visitor ids

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• 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 change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #49 (e3e5010) into dev-v2.0.1 (655ee79) will increase coverage by 8.10%.
The diff coverage is 100.00%.

@@               Coverage Diff                @@
##             dev-v2.0.1      #49      +/-   ##
================================================
+ Coverage         82.02%   90.13%   +8.10%     
- Complexity          293      323      +30     
================================================
  Files                15       15              
  Lines              1541     1520      -21     
  Branches            180      180              
================================================
+ Hits               1264     1370     +106     
+ Misses              184       81     -103     
+ Partials             93       69      -24     

Flag	Coverage Δ
unit-functional-tests	90.13% <100.00%> (+8.10%)	⬆️

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Impacted Files	Coverage Δ
...ng/mobile/analytics/internal/AnalyticsConstants.kt	100.00% <ø> (ø)
...ng/mobile/analytics/internal/AnalyticsExtension.kt	89.96% <ø> (+12.80%)	⬆️
...e/analytics/internal/AnalyticsRequestSerializer.kt	92.30% <100.00%> (+7.01%)	⬆️
...keting/mobile/analytics/internal/AnalyticsState.kt	92.70% <100.00%> (+22.52%)	⬆️

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