Updating Dragon4 to ensure the number buffer always provides a significant digit...

Updating Dragon4 to ensure the number buffer always provides a significant digit if one exists. (#25096)

* Updating Dragon4 to ensure the number buffer always provides a significant digit if one exists.

* Changing System.Number.RoundNumber to not round up floating-point numbers.

* Re-enabling the RealFormatterTestsBase CoreFX tests

* Updating Number.RoundNumber to take a isCorrectlyRounded parameter and to use IEEE compliant rounding for floating-point numbers.

* Change SinglePrecisionCustomFormat to 7, ensuring it matches the value used in netcoreapp2.1