Introduce TaskDataHandler

[shobhitagarwal1612]

Towards #2993

Introduces a wrapper class for handling task data values. Provides a way to subscribe for changes to the task value.

This is a no-op change. This will be integrated along with TaskSequenceHandler in DataCollectionViewModel in future CLs.

See #2993 (comment) for detailed description.

@scolsen @anandwana001 PTAL?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.50%. Comparing base (5d2e5ec) to head (7923270).
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2995      +/-   ##
============================================
+ Coverage     63.41%   63.50%   +0.08%     
- Complexity     1244     1254      +10     
============================================
  Files           267      268       +1     
  Lines          6513     6529      +16     
  Branches        913      915       +2     
============================================
+ Hits           4130     4146      +16     
  Misses         1796     1796              
  Partials        587      587              

Files with missing lines	Coverage Δ
...ndroid/ground/ui/datacollection/TaskDataHandler.kt	100.00% <100.00%> (ø)

[shobhitagarwal1612]

@anandwana001 @scolsen PTAL?