docs(sensor_plus): improve description of accelerometer

[cristian-barbarosie]

Description

I believe the description of the accelerometer in docs/sensors_plus/usage.mdx is not accurate.

I changed the description of AccelerometerEvent and UserAccelerometerEvent. See https://en.wikipedia.org/wiki/Accelerometer

The text is now rather long; I was unable to compress the information I find relevant in a shorter text.

I changed the order of the topics because I feel the presentation is more clear if we explain first the concept of acceleration in itself, and only after that we explain that the gravity is indistinguishable from an accelerated movement. I also changed the order in packages/sensors_plus/sensors_plus/example/lib/main.dart (perhaps this wasn't necessary).

I wonder if the descriptions of GyroscopeEvent and MagnetometerEvent are accurate and complete. I think at least the physical measure units should be mentioned. I suspect the GyroscopeEvent describes the rate of change of the rotation (angular velocity) rather than the rotation of the device. Or perhaps the angular acceleration ? Since I don't have enough knowledge on these topics, I left them unchanged.

Related Issues

Discussion #1419

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.

[nohli]

LGTM!
Thanks for your contribution! ❤️