Replace Modal.isOpen with controlled boolean

[mcous]

Overview

When writing the Modal component for prime-core, I suggested we ditch events in favor of the two-way data binding of an isOpen store. After some usage in the app, we've discovered this is a pretty awkward API.

This PR switches the modal back to a plain, controlled isOpen: boolean prop and a close event, which should be more predictable. As a result, this means the modal is no longer capable of closing itself; it must emit the close event and the parent must chose to close it.

I think there are continuing improvements to be made here, especially given the awkwardness of combining the close event with any buttons placed in the primary and secondary slots, but I think this is a step in the right direction.

This is a breaking change to prime-core. See the companion PR in the app: https://github.com/viamrobotics/app/pull/2873

Review requests

• Read through unit test updates
• Test out the playground
• Check storybook

[ehhong]

followed review requests and everything lgtm! the modal is not really visible in storybook but the code snippets look good

[anjinai]

lgtm too - Followed review requests and have the same comment as emily re: the modal not being visible in storybook.