Add ability to see both battery estimates on long press

If the enhanced estimate is being used in battery settings
it is now possible to long press on the text to have it display
both instead of the string that is normally used.

Adds another loader to enable this since it needs both the old
and the new estimates simultaneously.

Feature is hidden behind a feature flag that only googlers will
have enabled.

Test: robotests
Bug: 38399275
Change-Id: I5caf26513baada27efd50ddb0e72d3868da47150