feat(shared): expose rawChildrenMap in context

[jaulz]

This PR exposes the raw children map in the context so custom directives can do the same as v-html does:
https://github.com/vuejs/vue-next/blob/master/packages/compiler-ssr/src/transforms/ssrTransformElement.ts#L171

As a side effect it gets rid of this static (though weak) map:
https://github.com/vuejs/vue-next/blob/master/packages/compiler-ssr/src/transforms/ssrTransformElement.ts#L53-L56

[posva]

What feature is this implementing? If there isn't any, do you have a real world scenario that requires this change?

[jaulz]

@posva yep, like I mentioned this change will allow custom directives to do the same as v-html does. In my case I have a v-emojis directive that walks through it's children and replaces UTF-8 emojis with images (<img src="..." />). Since it is supposed to work in SSR context as well this is the only possible way that I found how it could possibly work. The v-html directive takes the expression and sets it in the rawChildrenMap (see https://github.com/vuejs/vue-next/blob/master/packages/compiler-ssr/src/transforms/ssrTransformElement.ts#L170-L171) but this map is not exposed anywhere so the v-html directive is the only directive that can take advantage of it.

Update: I forgot to say that this PR does not change any existing functionality and all tests are supposed to still pass (which they did in my local environment). This PR just exposes the map in the context so custom directives can make use of it.

[jaulz]

The failing test does not fail in my local environment...

[jaulz]

@posva any chance to have a look at it again after my explanation? thanks! 😊