GH-1311: Use Locale.ROOT when formatting JDBC interval strings

[Arawoof06]

What's Changed

formatIntervalYear and formatIntervalDay build the Oracle-style interval strings the JDBC interval accessor returns from getString()/getObject() with String.format and no explicit locale, so java.util.Formatter renders the %d digits using the JVM default locale. On a JVM whose default locale uses non-ASCII digits (ar-EG, bn-BD, mr-IN, ...) an interval comes back as +٠٢١-٠٢ instead of +021-02, which corrupts the value handed to JDBC clients and breaks anything parsing it as ASCII. Pass Locale.ROOT to both calls, the same fix GH-1300 applied to the C Data Interface format strings.

Closes #1311.