Implement MySqlDecimal

[sumitdvlp]

Hi,

The GetDecimal() or GetValue() functions of MySqlDataReader class are unable to handle very large value like
'1234567890123456789012345678901234567890123456789012345678901234.5'
They throw exception like value is too large because it return C# decimal datatype.

We saw MySQL connecter net has this functionality here. which return MySqlDecimal data type.

Can you please add method like GetMySqlDecimal which can support very large Decimal values.

[bgrainger]

MySqlDecimal documentation: https://dev.mysql.com/doc/dev/connector-net/8.0/api/data_api/MySql.Data.Types.MySqlDecimal.html

The primary operations appear to be:

• construct from a string (what validation is necessary?)
• .Value property that converts to decimal (that might throw for large values?)
• .ToDouble() that converts to a double (what happens if out of range?)
• .ToString() returns the original string

[sumitdvlp]

Created a PR #1075

[bgrainger]

Added in 2.1.0; thanks for the PR!