[SPARK-20211][SQL] Fix the Precision and Scale of Decimal Values when the...

[SPARK-20211][SQL] Fix the Precision and Scale of Decimal Values when the Input is BigDecimal between -1.0 and 1.0

### What changes were proposed in this pull request?
The precision and scale of decimal values are wrong when the input is BigDecimal between -1.0 and 1.0.

The BigDecimal's precision is the digit count starts from the leftmost nonzero digit based on the [JAVA's BigDecimal definition](https://docs.oracle.com/javase/7/docs/api/java/math/BigDecimal.html). However, our Decimal decision follows the database decimal standard, which is the total number of digits, including both to the left and the right of the decimal point. Thus, this PR is to fix the issue by doing the conversion.

Before this PR, the following queries failed:
```SQL
select 1 > 0.0001
select floor(0.0001)
select ceil(0.0001)
```

### How was this patch tested?
Added test cases.

Author: Xiao Li <gatorsmile@gmail.com>

Closes #18244 from gatorsmile/bigdecimal.