The Knicks are getting extra support in San Antonio from another New York athletic contingent in the Giants. Quarterback Jaxson Dart and receiver Odell Beckham Jr. — and possibly a few others — are expected to travel to Texas to cheer on the Knicks in the NBA Finals, sources told the The Post’s Ryan Dunleavy . The group was leaving the Giants’ practice facility in East Rutherford, N.J. and heading to Game 1. They’re expected to be back with Big Blue on Thursday. The Giants, current and alumni,