fix: Avoid leaks when using PictureRecorders

[st-pasha]

Description

When using PictureRecorder, the Picture object that it creates needs to be properly disposed after it is no longer used.

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]

It would be really nice to be able to have a custom lint rule that checks so that toImage isn't used, but I don't think that is possible (or not worth the amount of time it would take to fix that at least).

[erickzanardo]

LGTM