Fix inferring type of decimals with leading zeros in MongoDB

[nineinchnick]

Description

Trying to read collections with fractional decimal values like 0.03 was throwing an exception.

Java's BigDecimal.precision() returns precision for the unscaled value, so it skips leading zeros. SQL decimal's precision must include leading zeros in values less than 1.

Additional context and related issues

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# MongoDB
* Fix mapping MongoDB `Decimal128` values with leading zeros in decimal part. ({issue}`19068`)

[nineinchnick]

@SemionPar PTAL also, you're not in https://github.com/orgs/trinodb/teams/contributors so I can't add you as a reviewer. @wendigo @hashhar can you maybe add Semion there? Or only org admins can?

[hashhar]

People get added (automatically) after they've submitted and merged a PR. No exceptions.

[hashhar]

LGTM

It'll be useful to audit whether existing type mapping tests include values < 1 for other connectors as well. e.g. BigQuery also goes via BigDecimal (though we don't need to infer the precision and scale there).

[hashhar]

@ebyhr Do you want to take a look?