[C#] Map `number` to `Decimal`

[wing328]

Similar to Java which maps number to BigDecimal, we should do the same for C# to make it consistent across different langauges by mapping number to Decimal in C#.

If anyone has any concern or suggestion, please kindly voice out.

[jimschubert]

Would this be the same as #2813 , or would that issue then require an option to generate as Double instead? I think we had discussed this previously.

[wing328]

My understanding is that we need the following mapping:

float (type:number, format: float) => float
double (type: number, format: double) => double
number (type: number, no format) => decimal

(currently number is mapped to double as well)

[wing328]

#2813 has been closed due to no response from the user.