build: run ng update migrations for v12-next

[Splaktar]

• update StackBlitz for v12-next
• add v12-next to version list
• fix warnings about --prod being deprecated

build: update to Angular 12.0.0-next.5 and typescript 4.2.3

• this fixes the broken form-field examples

You can try it here: https://angularmaterial.dev/

[annieyw]

I think the stackblitz update is messing with the examples:
https://angularmaterial.dev/components/autocomplete/examples

[Splaktar]

Doh, that doesn't look good. Thank you for the heads up. I'll take a look later today after some meetings.

[Splaktar]

I looked into this some more and the autocomplete examples are broken on https://next.material.angular.io/components/autocomplete/examples as well. So this isn't an issue introduced with this PR, but I will look into resolving it.

[Splaktar]

So this is looking like either Angular core is broken or some edge case of how we dynamically load components is broken. I'm going to open a separate issue for this in angular/components since it seems related to how we generate component-examples.

[Splaktar]

Here's the issue to track these form-field example issues: angular/components#22285

[Splaktar]

OK, next.5 CLI build deployed as well. This should be ready to merge.