refactor(angular): drop support for angular < 13

[kroeder]

What I did

According to the Angular LTS plan, Angular 12
support ends in Nov 2022. A lot of code exists
to support Angular < 13 which increases the
maintenance effort and decreases the
contribution DX of framework/angular.

This PR removes all code related to Angular < 13 in preparation for Storybook 7.0

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

If your answer is yes to any of these, please make sure to include it in your PR.

[kroeder]

Example app is running perfectly fine and I think I found every code related to Angular < 13
There are a few more places tagged with "drop before storybook 7.0 release" but they are not related to the support of Angular < 13

@ThibaudAV any second thoughts? @ndelangen already agreed to this

This is the first PR of a smaller series with the goal to improve the DX for framework/angular in the repo. This also massively decreases the mental load and maintenance effort in the code base

[ndelangen]

I think a migration note in MIGRATION.md is warranted about this @kroeder 👍

[ThibaudAV]

🚀
Only thing to add is :
What about now always support only same supported version than Angular ? 😁
https://angular.io/guide/releases

Is more easy for many reason and try to support the last one as fast as possible

[kroeder]

🚀
Only thing to add is :
What about now always support only same supported version than Angular ? 😁
https://angular.io/guide/releases

Is more easy for many reason and try to support the last one as fast as possible

Since dropping support is a breaking change, storybook can only do this between major releases. Angular has 2 majors a year and supports the last 3, storybook has about 1 a year, right? So, most likely storybook would need support the last 4

But officially, I totally agree with you! We should only support all lts versions

@ndelangen @shilman I don't know with whom I already have discussed this on discord but anyway, should we do this? Only support angular lts? (basically 1 1/2 year of angular code)

If yes, where should we document this?

[kroeder]

I think a migration note in MIGRATION.md is warranted about this @kroeder 👍

@ndelangen I added a note to the MIGRATION.md - is this good enough?