[MOB-5589] Fix/null safety issues

[AliAbdelfattah]

Summary of Changes

• Update platformVersion return type to nullable for consistency with flutter latest plugin templates
• Remove (undo) result call on non-void return type values which fixes failing tests on iOS
• Update Crash Reporting to use null-aware operators
• Update package metadata as per the guidelines of pub.dev
• Update package min flutter version to 1.17 instead of 2.0
• Update package version
• Update sample app pubspec
• Bump Flutter SDK version used on CI from 1.20.4 to 2.2.3
• Bump mockito version
• Regenerate mocks
• Fix CI broken build scripts after updating the Flutter SDK version
• Increase network logger tests coverage

TODO:

• Fix CI broken build scripts after updating the Flutter SDK version.
• Increase test coverage

[InstabugCI]

	1 Warning
⚠️	Please include a CHANGELOG entry. You can find it at CHANGELOG.md.

Generated by 🚫 Danger

[codecov]

Codecov Report

Merging #184 (cb71e91) into feature/null-safety (3b227bf) will decrease coverage by 5.90%.
The diff coverage is 59.33%.

@@                   Coverage Diff                   @@
##           feature/null-safety     #184      +/-   ##
=======================================================
- Coverage                69.21%   63.31%   -5.91%     
=======================================================
  Files                       14       14              
  Lines                      484      447      -37     
=======================================================
- Hits                       335      283      -52     
- Misses                     149      164      +15     

Impacted Files	Coverage Δ
lib/NetworkLogger.dart	0.00% <0.00%> (ø)
lib/models/network_data.dart	0.00% <0.00%> (ø)
lib/utils/http_client_logger.dart	0.00% <0.00%> (ø)
lib/Surveys.dart	51.06% <47.05%> (ø)
lib/CrashReporting.dart	69.23% <55.55%> (+2.56%)	⬆️
lib/Replies.dart	54.83% <56.00%> (ø)
lib/BugReporting.dart	52.17% <59.25%> (-7.29%)	⬇️
lib/Chats.dart	71.42% <60.00%> (ø)
lib/FeatureRequests.dart	77.77% <71.42%> (-4.05%)	⬇️
lib/InstabugLog.dart	89.47% <75.00%> (ø)
... and 3 more

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