Remote device battery level reported incorrectly

Per HFP specs, the AG reports battery level via CIND/CIEV with value
ranging from 0 to 5. RemoteDevices#updateBatteryLevel expects battery
level to be a percentage (i.e., an integer from 0 to 100).

In onAgIndicatorValueChanged, the integer from
BluetoothHeadsetClient.EXTRA_BATTERY_LEVEL is passed directly into
updateBatteryLevel. It needs to be converted into a percentage first.
For example, if the remote device has a full charge,
BluetoothHeadsetClient.EXTRA_BATTERY_LEVEL returns a 5, but this then
gets reported as 5% instead of 100%.

onHfIndicatorValueChanged will be left unchanged. Per HFP specs, the HF
reports battery level via BIND/BIEV with value ranging from 0 to 100.

Tag: #refactor
Bug: 219517423
Test: atest RemoteDevicesTest
Test: atest BluetoothInstrumentationTests
Test: manually verify a full battery is reported as 100% instead of 5%
Ignore-AOSP-First: see 16809739
Change-Id: I0c0453537905b33c78e405d3889f2de5d3e6cc57