feat: useViewModelInstance use name and artboardName when getting vmi from a file

[mfazekas]

Summary

Fixes #124 - useViewModelInstance hook now correctly handles the name parameter:

• name consistently means ViewModel instance name (not ViewModel class name) for both RiveFile and ViewModel sources
• New artboardName param for RiveFile source to specify which artboard's ViewModel to use
• TypeScript overloads enforce param availability by source type (e.g., artboardName only available for RiveFile)

Test plan

• Unit tests pass (yarn test)
• TypeScript compiles (yarn typecheck)
• Lint passes (yarn lint)
• Harness tests on device

[HayesGordon]

LGTM! I left one comment, but this is something we will address in the ideal API when we adopt the new iOS and Android runtimes.

[HayesGordon]

I like this, but I'm worried that we now have many ways to do the same thing. You could get the correct vmi by doing:

const viewModel = riveFile?.viewModelByName('My View Model');
const namedInstance = useViewModelInstance(viewModel, { name: 'My Instance' });

I'm worried that if we expose this convenience, we bury this usage. Which is important when you're working with lists.

But I see the convenience of this. Ideally, with the future API where you will have the Artboard and State Machine configured before creating the view, this additional parameter won't be needed as the artboard will already be known by then.

[mfazekas]

one option is extending the options to useViewModelInstance(file, { options })

so there could be artboardName, viewModelName and instanceName.

In this PR it's arboardName and name (instead of instanceName). But instanceName would be better - more explicit.

const viewModel = riveFile?.viewModelByName('My View Model');
const namedInstance = useViewModelInstance(viewModel, { name: 'My Instance' });

Yep that's works too. The only thing is that since const viewModel = riveFile?.viewModelByName('My View Model'); is not a hook there is a decision the user has to make if he wants to memoize it or not. Probably doesn't matter as viewModelByName is very fast I'd assume.

This would be the equivalent:

const namedInstance = useViewModelInstance(viewModel, { modelName: 'My View Model', instanceName: 'My Instance' });