BLE scan time optimization

BLE scan time optimization to reduce scan latency:
1)Reduce scan interval and window for low power, balanced and ambient scan modes. Balanced and ambient modes now have effectively the same settings.
2)Add screen off and screen off balanced modes with longer interval  for the internal use.
3)For regular apps:
   Foregroud: original scan mode.
   Background + screen on: low power mode.
   Screen off: screen off mode.
  For foreground service:
   Screen on: original scan mode.
   Scree off: fall back to screen off/screen off balanced mode unless it
   requests low latency mode.
4)When App requests a new scan without recent request, its scan mode is
upgraded temporarily for 6 seconds (configurable).

Tag: #feature
Bug: 214595841
Test: Run scan in low power, low latency and balanced scan modes with filtered and unfiltered settings both continuously and periodically.

Make sure the scan mode is set correctly during screen on/off transition and background/foreground transition.

Tested with multiple scan clients from both test app and other service apps.

Change-Id: I291a1a80f24d431b681aae485692241dfb474c5a

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