Extract logic for constructing ApiRequest from ApiService

[fractalwrench]

Goal

Extracts the logic for constructing ApiRequest objects into a separate file. This makes it easier to unit test the business logic for mapping events/sessions to ApiRequest.

This is necessary for future work that will give failed request types different priorities on the retry queue. This is mostly just a case of lifting functions into a separate source file, although I did remove/alter some redundant code in a couple of functions.

Testing

Added unit test coverage.

[codecov]

Codecov Report

Merging #61 (a511645) into master (9034693) will increase coverage by 0.25%.
The diff coverage is 82.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #61      +/-   ##
==========================================
+ Coverage   75.74%   75.99%   +0.25%     
==========================================
  Files         308      309       +1     
  Lines       10067    10057      -10     
  Branches     1452     1448       -4     
==========================================
+ Hits         7625     7643      +18     
+ Misses       1851     1826      -25     
+ Partials      591      588       -3     

Files	Coverage Δ
...mbracesdk/comms/delivery/EmbraceDeliveryService.kt	60.83% <0.00%> (ø)
.../android/embracesdk/comms/api/EmbraceApiService.kt	82.05% <88.88%> (+5.35%)	⬆️
...e/android/embracesdk/comms/api/ApiRequestMapper.kt	82.22% <82.22%> (ø)

... and 2 files with indirect coverage changes

[bidetofevil]

Oh yeah this is nice. It'll work well with the changes I had and replace the clunky map I have!