fix(compiler): nested scoped slot not update (fix #12232, #12245)

[JuniorTour]

	Before Fix	After Fix
Issue	Fix #12232
Reproduction Link	https://jsbin.com/sakiwam/edit?html,output	https://jsbin.com/rexakik/edit?html,output
Screenshot
Issue	Fix #12245
Reproduction Link	https://codesandbox.io/s/vue-2-x-reactivity-broken-tqogh	https://jsbin.com/gatanir/edit?html,output
Screenshot

What kind of change does this PR introduce? (check at least one)

• [x] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• [x] It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• [x] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• [x] All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• [x] New/updated tests are included

If adding a new feature, the PR's description includes:

• [ ] A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

[hivokas]

Great!

[hivokas]

Is there anything that prevents this PR from being merged? 👀 It fixes the issue I have in the app I'm working on.

[JuniorTour]

Is there anything that prevents this PR from being merged? 👀 It fixes the issue I have in the app I'm working on.

We have to wait for code review and approval from official maintainer. 🤷‍♂️

[trevorgehman]

Curious if this will be merged? It seems to fix the discrepancy between the old and new slot syntax, which is breaking some reactivity for us within nested slots.

[shengnoyi]

Is there any plan for when to merged this?