[fix](type) fix DECIMAL scale when cast function on fe

[nextdreamblue]

Proposed changes

Issue Number: close #12717

Problem summary

根据cast传递的DECIMAL类型的精度来处理DECIMAL数据.

before: MySQL [test]> select cast('135.759999999' as DECIMAL(10,3)); +----------------------------------------+ | CAST('135.759999999' AS DECIMAL(10,3)) | +----------------------------------------+ | 135.759999999 | +----------------------------------------+ 1 row in set (0.00 sec)

now: MySQL [stage]> select cast('135.759999999' as DECIMAL(10,3)); +----------------------------------------+ | CAST('135.759999999' AS DECIMAL(10,3)) | +----------------------------------------+ | 135.759 | +----------------------------------------+ 1 row in set (0.01 sec)

Checklist(Required)

1. Does it affect the original behavior:
   • [x] Yes
   • [ ] No
   • [ ] I don't know
2. Has unit tests been added:
   • [ ] Yes
   • [ ] No
   • [x] No Need
3. Has document been added or modified:
   • [ ] Yes
   • [ ] No
   • [x] No Need
4. Does it need to update dependencies:
   • [ ] Yes
   • [x] No
5. Are there any changes that cannot be rolled back:
   • [ ] Yes (If Yes, please explain WHY)
   • [x] No

Further comments

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