refactor!: bullet getter and setter

[alestiago]

Description

Removes setBullet and isBullet in favour of setter and getters.

// Before:
body.setBullet(true);
body.isBullet(); // true

// After:
body.isBullet = true;
body.isBullet; // true

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

[spydon]

@alestiago should I close the two open PRs until you get back to them?

[alestiago]

I can get to them, I'll make some time for it between this and next week.

It is ready for a re-review. Once this is merged I will take a look at the other one.