[sensors] Change Android implementation to use SENSOR_DELAY_GAME, …

[mikeryder]

…which is approximately 50Hz. For reference the iPhone implementation is still sending updates faster at 100Hz.

Update Gravity constant to be more precise.

Description

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Related Issues

*flutter/flutter#25971 - This PR does not fix the issue entirely because the issue is requesting parameters for the frequency of sensor updates, but at least brings the refresh rates of iOS and Android closer until the larger PR with parameters is accepted. *

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[stuartmorgan-g]

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