Compat support: toNumber, toString, string/array ops

[towerofnix]

Follow-up to #157, supports leopard-js/sb-edit#90. These too are needed for comprehensive Scratch compatibility. (toString technically isn't, but it's cleaner to use consistent casting methods.)

[towerofnix]

@adroitwhiz Changes here should be ready for implementation into #146. They're basically all lifted from scratch-vm.

[PullJosh]

@towerofnix Time for a version bump and new release? If you update the version number with npm version and push those changes to Github, we can create a new release on Github and an action will automatically publish to npm.

Thank you so much for all this work, by the way! And apologies for taking so long to review. Life gets busy 😰

[towerofnix]

Sounds good! I'll give it a version and push. And it's all OK, @adroitwhiz's and my work here all started and ramped up pretty spontaneously so we weren't expecting quick reviews ^_^

[towerofnix]

I'm going to give sb-edit a dependencies update locally and then I'll get both of 'em pushed.

[PullJosh]

Sweet! sb-edit also has the automatic npm publishing set up, so I think the only thing you need me for is redeploying the website after sb-edit has been published. :)