Use ImeAwareEditText in FingerprintSettings

Like we did the same thing in the Settings app [1][2][3],
FingerprintSetting is another instance that should use
ImeAwareEditText to make sure InputMethodManager#showSoftInput() is
called after the EditText gains IME focus.

This approach should be more robust and easier to maintain than trying
to control the software keyboard visibility with
SOFT_INPUT_STATE_ALWAYS_VISIBLE, which is more complicated that people
think.

This CL also removes RenameDialog#mTextHadFocus since
RenameDialog#mDialogTextField is always focused when the dialog is
shown [4].

This CL also removes the following fields since they can just be a
local final variables that will be captured into callback.

 * RenameDialog#mFingerName
 * RenameDialog#mTextSelectionStart
 * RenameDialog#mTextSelectionEnd

 [1]: I182b05d3ff59fb3b4732d60d0d5a464f0e0e0235
      f6af093e
 [2]: I892d639f3cc5d43db553b682d5278b8ce2fe72da
      48032671
 [3]: Ib75ba0f361b8b46c3b717cc1ffb864726958ed82
      b0bcbed3
 [4]: I5bb1b7227c1323595bf7f483e11e87e2c3550093
      7a1d52eb

Fix: 118473687
Test: Manually verified as follows.
      1. Build and flash aosp_taimen-userdebug to Taimen
      2. Set up a fingerprint unlock.
      3. Rotate the device to landscape mode.
      4. Open Settings -> Security & location -> Fingerprint
      5. Re-enter password if necessary
      6. Tap "Finger 1"
      7. Make sure that AOSP Keyboard shows up
Change-Id: I2a137aa8f6a1ee2b67923bcf40e82320a56c7b59