FormArray is incorrectly pristine

Which @angular/* package(s) are the source of the bug?

forms

Is this a regression?

Yes

Description

I have a FormArray containing a FormGroup containing a FormControl. When a FormControl is edited (by the user through an input), the FormGroup is correctly set as dirty, but the FormArray incorrectly stays pristine.

Please provide a link to a minimal reproduction of the bug

https://embed.plnkr.co/plunk/MemMp3sni5MEtdSV

Please provide the exception or error you saw

No response

Please provide the environment you discovered this bug in (run ng version)

Angular CLI: 12.2.2
Node: 14.19.1
Package Manager: npm 
OS: linux x64

Angular: 12.2.2
... animations, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1202.2
@angular-devkit/build-angular   12.2.2
@angular-devkit/core            12.2.2
@angular-devkit/schematics      12.2.2
@angular/cdk                    10.2.7
@angular/flex-layout            12.0.0-beta.34
@angular/google-maps            12.2.11
@angular/material               10.2.7
@schematics/angular             12.2.2
rxjs                            6.6.7
typescript                      4.3.5

Anything else?

No response

[dylhunn]

adding a setter might be the right choice here

I’m sort of inclined to agree, but it’s going to cause massive breakage unfortunately. The docs we can fix though.

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