fix(forms): changes to status not always being emitted to statusChanges observable for async validators.

[dylhunn]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

When a FormControl, FormArray, or FormGroup is first constructed, if an async validator is attached, the statusChanges observable should receive a message when the validator complete (i.e. pending -> valid/invalid).

Issue Number: 42553

What is the new behavior?

If the validator was provided as part of the constructor options, it was previously not fired at construction time. That is fixed in this PR.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Fixes #42553

[AndrewKushnir]

Just as an additional context: the original changes were added in PR #38354 (we can look at that PR to see which tests we should add in this PR).

[dylhunn]

For reference, here's a TGP run: https://test.corp.google.com/ui#id=OCL:378802147:BASE:378802259:1623386981464:3da3dae8

While there is breakage, it's a very limited amount which can probably be fixed by hand.

[dylhunn]

TGP was green (surprisingly) after rerunning flakes. Also updated the issue number in the original PR, which was incorrect.

[AndrewKushnir]

Thanks for the fix @dylhunn 👍
The changes look good, I've just added a few minor comments related to tests.

[AndrewKushnir]

@dylhunn FYI I've also added the target: patch label, since it should be safe to land in the next patch version, given that the TGP is fully green.

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