function makeContentJumpBuffers(subtree) {
  const contentJumpBuffers = subtree._contentJumpBuffers;
  const contentAvailabilityBitstreams = subtree._contentAvailabilityBitstreams;
  for (let i = 0; i < contentAvailabilityBitstreams.length; i++) {
    const contentAvailability = contentAvailabilityBitstreams[i];
    const contentJumpBuffer = makeJumpBuffer(contentAvailability);
    contentJumpBuffers.push(contentJumpBuffer);
  }
}
Make the jump buffers, i.e. maps of bit indices to the metadata entity IDs,
for the content metadata. This is stored in the subtree.

@param {ImplicitSubtree} subtree The subtree
@private