Implement the Decimal Module of the Morphir IR SDK

**Is your feature request related to a problem? Please describe.**
Morphir's SDK seeks to have parity with much of elm/core and should have full parity with elm/core Decimal.

**Describe the solution you'd like**
Implement the functions in [elm/core Decimal](https://github.com/finos/morphir-elm/blob/main/src/Morphir/IR/SDK/Decimal.elm) and add tests. Over time we will add more functionality here, but this is a good start.

**Describe alternatives you've considered**
N/A

**Additional context**
N/A