[refactor] Remove Decmial Type and rename DecmialV2 to Decimal

[yangzhg]

Since the Decmial type has been depracted for a long time and has not been used in actual use, DecmialV2 has been widely used, so we plan to remove the Decmial related code and rename DecmialV2 to Decimal
The work will be divided into two parts,

• the first will remove the decimal related code,
• the second will rename decimal V2 to decimal