[WIP] Reimplementing tansu with signal-polyfill

[divdavem]

This PR is an experimental new implementation of tansu based on signal-polyfill. It is still a work-in-progress.

The long-term goal is to increase interoperability with other signal libraries, so that it is possible, for example, to have a tansu store directly interpreted as reactive in an Angular computed, without having to first convert it to an Angular signal.

This PR currently relies on a modified version of signal-polyfill with the following fixes I suggested:

• Don't recompute when dependent signals come back to previous values used for last computation proposal-signals/signal-polyfill#15
• fix: it should not break a computed signal to watch it before getting its value proposal-signals/signal-polyfill#16
• Use prepare script allowing usage from git npm dependency proposal-signals/signal-polyfill#18
• Rewriting graph implementation, a signal is made live while getting its value proposal-signals/signal-polyfill#32
• Stabilize computed that calls set, reimplementation proposal-signals/signal-polyfill#34

This PR removes support for the pauseSubscribers and resumeSubscribers methods of the Store class, but otherwise tries to be as much as possible compatible with the current tansu implementation.