Enrich expression API

[mitikov]

Adding primitive APIs to reduce the volume of boilerplate code to be written while working with expressions.

Inspired by #70

[mitikov]

@arnaudleclerc Could you please review?

Thanks.

[codecov-commenter]

Codecov Report

Merging #71 (bccadbc) into develop (8393100) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop      #71   +/-   ##
========================================
  Coverage    86.45%   86.45%           
========================================
  Files          124      124           
  Lines         3655     3655           
========================================
  Hits          3160     3160           
  Misses         495      495           

Flag	Coverage Δ
unittests	86.45% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...rc/AzureMapsControl.Components/Atlas/Expression.cs	96.15% <ø> (ø)

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[arnaudleclerc]

@mitikov Thanks for the PR, this is a great improvement! Everything looks fine.

Do you think it is possible to add some unit tests on the new code ?

[mitikov]

@arnaudleclerc Sure, here you go :)

[arnaudleclerc]

Awesome, thank you!