support cast to decimal data type in datafusion

[liukun4515]

Is your feature request related to a problem or challenge? Please describe what you are trying to do. In the #122 , we need to support the decimal data type.

In order to support column_a > 12 for the decimal data type, we need to support the cast/try_cast first. For some operations, such as comparison operations and mathematics operations, we need to convert some numeric data types to decimal first.

TODO

• [x] signed numeric to decimal https://github.com/apache/arrow-datafusion/pull/1442
• [ ] utf-8 to decimal
• [x] decimal to signed numeric https://github.com/apache/arrow-datafusion/pull/1465
• [x] remove duplicated code for cast/try_cast code https://github.com/apache/arrow-datafusion/pull/1465#pullrequestreview-853170945
• [x] decimal to diff decimal https://github.com/apache/arrow-datafusion/pull/1603

The unsigned numeric is not the standard data type in SQL, we no need to support them. @alamb

Some parts in arrow-rs: https://github.com/apache/arrow-rs/issues/1043

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[liukun4515]

please assign this issue to me.