Update synthetic password terminology to match new design doc

Update terminology to eliminate ambiguity and to match
http://go/android-locksettings-design :

- The class that represents a synthetic password is now called
  SyntheticPassword instead of AuthenticationToken.  This eliminates an
  inconsistency and avoids ambiguity with the other types of
  authentication tokens (HardwareAuthTokens and escrow tokens).

- "LSKF" is now used in preference to "password", which could be
  confused with LSKFs of type password and with the many other types of
  password (synthetic, Keystore, Gatekeeper).  "Password" is still used
  in places like "password data", "password metrics", and "password
  history"; renaming those in the design doc and code is left for later.

- The things that protect the SP are now called "SP protectors", or just
  "protectors" when SP is clear from context.  Previously these were
  called "synthetic passwords" (ambiguous with the SP) or "SP blobs"
  (ambiguous with the spblob file, which is just part of a protector).

- The 64-bit integers that identify protectors are now called "protector
  IDs" instead of "synthetic password handles".  This avoids ambiguity
  with the SP's Gatekeeper password handle (which in the code is just
  called a "synthetic password handle"; a later CL might clarify that),
  and it clarifies that the identified items are SP protectors, not SPs.

- The secret that each protector uses to protect the SP is now called
  the "protector secret" instead of the application ID.  This avoids
  ambiguity with the Keystore application ID, which isn't being used and
  is a less intuitive name.

No behavior changes intended, except for some changed log messages.

Test: atest com.android.server.locksettings
Test: Basic manual test of locksettings core functionality: upgraded a
      device that has a pattern set, without wiping userdata; unlocked;
      changed to PIN; rebooted; unlocked; changed to swipe; rebooted;
      changed to password; rebooted; and unlocked.
Change-Id: I564a738119a47a31b4822d26c6405249f8ce1c06