This commit relaxes the type of the `formControlName` input to accept both a `string` and a `number`.
Currently, when using a `FormArray`, most templates look like:
```
<div formArrayName="tags">
<div *ngFor="let tag of tagsArray.controls; index as i">
<input [formControlName]="i">
</div>
</div>
```
Here `formControlName` receives a number whereas its input type is a string.
This is fine for VE and `fullTemplateTypeCheck`, but not for Ivy which does a more thorough type checking on inputs with `fullTemplateTypeCheck` enabled and throws `Type 'number' is not assignable to type 'string'`. It is fixable by using `formControlName="{{i}}"` but you have to know the difference between `a="{{b}}"` and `[a]="b"` and change it all over the application codebase. This commit allows the existing code to still type-check.
PR Close#30606
628b0c1154