Address review suggestions for sensor direct report related APIs

Changes inline with bug number

Some improvements about SensorDirectChannel class.
  * Complete the doc about creation of SensorDirectChannel object.
  * Make SensorDirectChannel implements java.nio.channels.Channel.
  * Change isValid() to isOpen().
  * Make close() thread safe.
Bug: 36550285

  * Throw exception on failure of SensorManager.createDirectChannel.
  * Change to use NullPointerException when unexpected null pointer
    is passed in.
Bug: 36555061

  * Move SensorManager.configureDirectChannel() to
    SensorDirectChannel.configure().
  * Format SensorDirectChannel.configure() function doc with
    <pre></pre> to maintain the table structure.
  * Reworded Sensor.isDirectChannelTypeSupported java doc.
Bug: 36555604

Test: pass updated cts SensorDirectReportTest
Change-Id: I447121eaf414cbc94292a109a9d93d2e3c89f8f4