Backport 3-arg `rand` to AbstractPPL 0.5.x

[sunxd3]

rand defaults have been added since AbstractPPL v0.6.2 (#79), backporting to v0.5 for compatibility.

[yebai]

Thanks, @sunxd3 -- it looks good; feel free to merge once CI passes.

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (releases-0.5.x@d6d898b). Click here to learn what that means. Patch has no changes to coverable lines.

Additional details and impacted files

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[devmotion]

For future backports, a common approach (that we use e.g. also in SpecialFunctions) is to cherry-pick the relevant commit. See e.g. https://github.com/JuliaLang/julia/blob/a77ba79855f400420ccaa09c153ecec2784e386e/doc/src/devdocs/build/distributing.md#cherry-picking-commits for an explanation. The advantage is that one can then resolve conflicts similar to merges and git copies information such as the original commit message and contributors.

[sunxd3]

The changes were done by local git cherry-pick, somehow the original commit information was lost still, I'll verify next time.