Parquet: schema validation should allow scale == precision for decimal type

[sunchao]

Which issue does this PR close?

Closes #1606.

Rationale for this change

For decimal type, it is a valid case for scale to be equal to precision. However currently the PrimitiveTypeBuilder will return error in such case.

        if self.scale >= self.precision {
            return Err(general_err!(
            "Invalid DECIMAL: scale ({}) cannot be greater than or equal to precision \
             ({})",
            self.scale,
            self.precision
        ));

It seems the Parquet logical type specification for decimal type is also incorrect on this:

If not specified, the scale is 0. Scale must be zero or a positive integer less than the precision. Precision is required and must be a non-zero positive integer. A precision too large for the underlying type (see below) is an error.

Both Java and C++ implementation allows scale to be equal to precision.

What changes are included in this PR?

Fix the schema validation and allow the case when scale is equal to precision. Added a test for this.

Are there any user-facing changes?

• Yes, the behavior is fixed after the PR, where users can now construct decimal logical type where scale is equal to precision, such as Decimal(5, 5).
• There is no API change introduced.

[sunchao]

cc @viirya @alamb @nevi-me could you help to review this? thanks

[viirya]

Hmm, I think decimal(5, 5) is valid but it sounds a bit weird that the spec is incorrect but the implementations are correct. Should we update the Parquet spec too?

[viirya]

Based on what I can get, this should be correct. I have no idea why the Parquet spec has defined scale must be less than precision, but looks like the known implementations don't follow it...