fix(module: textarea-item) fix ngModel

[sharky556]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd-mobile/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?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

When a textarea is entered with a value, this._onChange is triggered in both of the following places, which causes the value of the form control to be triggered twice, leading to a number of problems

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[aijunhao]

I'm sorry, I can't reproduce the problem you mentioned. Can you give me a demo on StackBlitz?

[sharky556]

I'm sorry, I can't reproduce the problem you mentioned. Can you give me a demo on StackBlitz?

When the value of the textarea input changes, you can see that the ngModelChange method is triggered twice, which doesn't look quite normal.
https://stackblitz.com/edit/angular-hrkf1c?file=src%2Fapp%2Fapp.component.ts