Unit test failure when JVM default charset is not UTF-8

The changes done in CALCITE-1103 (potentially along with the new test for unicode column names in CALCITE-835) was causing failures on some ASF jenkins hosts.

In TypedValue, when serializing a String in a the Protobuf variant of TypedValue, the resulting bytes were platform dependent, instead of always specifying UTF-8. Protobuf requires UTF-8 bytes for the method we were invoking, and, thus, threw an exception.