Make ScanTerm immutable

Suggested Release Note: NONE

Previously, a ScanTerm could be modified by setting elements of the array returned by `id()`. The MINIMUM_PATTERN and MINIMUM_PATTERN "constants" could be mutated in this way too, either by directly modifying the public static array or by modifying the array returned by `ScanResult.minimum().id()`.

To make ScanTerm fully immutable, the constructor should make a defensive copy of the "id" byte array, and the id() method should also return a copy of the array.