Fix JSON serialization of quantities with decimal values

[rohahn]

Add IDecimalQuantity interface to expose the decimal value
Serialize decimal values as string to keep number of decimal places

[codecov]

Codecov Report

Merging #868 (e9a8161) into master (4993a2a) will decrease coverage by 0.35%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #868      +/-   ##
==========================================
- Coverage   83.09%   82.74%   -0.36%     
==========================================
  Files         287      287              
  Lines       42987    43332     +345     
==========================================
+ Hits        35720    35853     +133     
- Misses       7267     7479     +212     

Impacted Files	Coverage Δ
...Serialization.JsonNet/UnitsNetBaseJsonConverter.cs	100.00% <100.00%> (ø)
UnitsNet/GeneratedCode/Quantities/BitRate.g.cs	85.43% <100.00%> (+0.09%)	⬆️
UnitsNet/GeneratedCode/Quantities/Information.g.cs	86.09% <100.00%> (+0.09%)	⬆️
UnitsNet/GeneratedCode/Quantities/Power.g.cs	85.20% <100.00%> (+0.10%)	⬆️
UnitsNet/GeneratedCode/Quantity.g.cs	52.00% <0.00%> (-29.41%)	⬇️
UnitsNet/CustomCode/Quantity.cs	81.08% <0.00%> (-3.13%)	⬇️
UnitsNet/QuantityTypeConverter.cs	98.38% <0.00%> (-0.03%)	⬇️
UnitsNet/GeneratedCode/Quantities/Length.g.cs	94.00% <0.00%> (+0.02%)	⬆️
UnitsNet/GeneratedCode/Quantities/VolumeFlow.g.cs	90.01% <0.00%> (+0.03%)	⬆️
... and 102 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4993a2a...e9a8161. Read the comment docs.

[angularsen]

Solid work on this 👏 Love the tests!

I think it is clever to use string to support decimal, but I'm concerned we are breaking backwards compatibility on the JSON schema for those expecting to read Value as a number.

How about this:

• Keep Unit and Value exactly as before, the double representation of the number matching our common public interface for quantities.
• If value is not double, then add two more fields
  • ValueString with textual representation of number
  • ValueType with string values like "decimal", "float", "SomeLibrary.BigInt"

This makes the schema more extensible to other types of numbers with generics, as have been discussed a number of times:
#180
#285
#666
#714

[rohahn]

I implemented your proposal.

[angularsen]

Looks perfect to me, great work on this!

[angularsen]

Nuget is on the way out, I'd appreciate it if you gave it a spin to ensure it works as expected and comment back here! 🙇
Release JsonNet/4.3.0 · angularsen/UnitsNet

[rohahn]

Why is the version number 4.3.0?

[angularsen]

JsonNet nuget is versioned separately from UnitsNet nuget, but they share major version.