fix: (platform) fix for textarea breaking

[kavya-b]

Please provide a link to the associated issue.

#3086

Please provide a brief summary of this pull request.

• FormMessage had to be imported in the docs for one of the examples, without which the 'without Platform Forms' example was showing some broken form message styling.
• Removed custom class added to example
• The ElementRef being used was, for some reason, not able to get the component's reference. This was fixed by using the read attribute.
• Fix for width issue by overriding the fd-popover styles. A similar fix is already being used in core.
• Using only required FormControlModule iinstead of loading entire core FdFormModule in textarea module.

Please check whether the PR fulfills the following requirements

• the commit message follows the guideline:
  https://github.com/SAP/fundamental-ngx/blob/master/CONTRIBUTING.md
• all items on the PR Review Checklist are addressed :
  https://github.com/SAP/fundamental-ngx/wiki/PR-Review-Checklist

Documentation checklist:

• Documentation Examples
• Stackblitz works for all examples

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[KevinOkamoto]

Looks good.

[droshev]

• The overlay is not properly attached to the text

area

There are cases where it is fine

• first click on a textarea with message shows the message shifted:
  

[kavya-b]

• The overlay is not properly attached to the text

area
There are cases where it is fine

• first click on a textarea with message shows the message shifted:
  

@droshev This seems to be a problem with the form-message handling at the Platform Forms level and needs to be explored. I have created issue #3229 for this and will look into this at a later point after the release. Since this PR needs to go through for release and these issues are not blocking, please approve it.

separate issue created for other form message related issues as mentioned in the previous comment. Dismissing this to unblock merging.