Update codebase to vue 3

[kaelonR]

This PR converts the code for vue-functional-data-merge to the new Vue 3 format for VNode props ($attrs object in component instances), addressing PRs #18 and #19.

To make this possible, the following changes have been made:

• VNodeData interface is now Record<string, unknown>, as per Vue's internal typing of the $attrs object.
• directives case has been removed (is now a withDirectives wrapper function in vue 3, and no longer part of the vnode binding)
• staticClass case has been removed, as this is now part of the class binding in Vue 3
• introduced a new mergeClass function which can merge class objects in the new vue 3 format
• attrs, props, domProps, scopedSlots, staticStyle, hook, transition, slot, and tag cases have been removed, as these properties are now either obsolete or have been flattened to sit directly under $attrs. only id, key, ref and keepAlive props have been retained to avoid overwriting these.
• nativeOn case has been removed, as in vue 3 the .native modifier no longer exists (events are now native by default when the component does not recognize them)
• a new check has been added outside the switch checking if a property starts with 'on', signifying that it's an event listener. event listeners use the same merge strategy as the 'on' object in Vue 2.
• Updated unit tests to match the new situation in Vue 3.
• removed vue from the package.json dependencies, as vue-functional-data-merge now no longer depends on anything from vue in order to function.

I did not update the version number in package.json, as I feel that it's your authority to decide what the next version number should be.

[coveralls]

Coverage increased (+3.8%) to 100.0% when pulling a80299d on J141:feat/vue3 into 7a217ca on alexsasharegan:master.

[alexsasharegan]

Thanks for the work on this! I'll go ahead and merge it into a new branch for Vue 3, and then review it and publish.

[alexsasharegan]

introduced a new mergeClass function which can merge class objects in the new vue 3 format

What do you mean by this? It appears to me that this new behavior is incorrect from maintaining a pure concatenation in order to preserve order for overrides.

[alexsasharegan]

https://github.com/vuejs/vue-next/blob/master/packages/shared/src/normalizeProp.ts#L59-L78

I believe this is the relevant code for Vue's internals to collapse class bindings. You'll notice it's recursive and should handle the old concat strategy and not require the object merge strategy here. I'm going to revert that behavior.

No worries on this of course, I'm super thankful you took the initiative to get everything started!

[alexsasharegan]

Available as vue-functional-data-merge@next

npm info vue-functional-data-merge@next