refactor!: used setters and getters for motorSpeed

[alestiago]

Description

Removes setMotorSpeed and getMotorSpeed from RevoluteJoint, PrismaticJoint and WheelJoint in favour of dart's setters and getters.

The following snippet illustrates the API change.

joint.setMotorSpeed(2); // OLD
joint.motorSpeed = 2; // NEW

joint.getMotorSpeed(); // OLD
joint.motorSpeed; // NEW

Checklist

• The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• I have read the Contributor Guide and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples.

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

Related Issues

[alestiago]

@spydon , CI/CD seems to be failing. Updated #47 to fix this.

[spydon]

Lgtm! A test that checks that the body is awake after setting the speed would be good too (for possible future regressions).