Some cleanup of the System.Number class (dotnet/coreclr#20619)

Some cleanup of the System.Number class (dotnet/coreclr#20619)

* Formatting Number.Formatting.cs and Number.Parsing.cs

* Removing some duplicated parsing code by having the Parse method call TryParse

* Moving two constants from NumberBuffer to Dragon4

* Rename FloatPrecision to SinglePrecision

* Updating the casing of the NumberBuffer fields

* Updating NumberBuffer to allow taking a custom-sized digit buffer.

* Updating the various NumberBufferLength constants to be the exact needed lengths

* Fixing DoubleNumberBufferLength and SingleNumberBufferLength to account for the rounding digit.

* Fixing TryParseNumber to use the correct maxDigCount

* Ensure the TryParseSingle out result is assigned on success

Commit migrated from https://github.com/dotnet/coreclr/commit/aef0bc27daebb70ccc4bdb9bd46960b7e8b5eb0e