chore(textarea): moving ios+md specific margin to native file (#30984)

Issue number: resolves internal

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->
The Ionic Textarea component, has a margin to avoid the textarea element
to overlap the label when the label placement is stacked. However, as
the ionic theme already has other styles that safeguard the label, this
margin, is causing a misalignment of the content:
<img width="457" height="174" alt="image"
src="https://github.com/user-attachments/assets/f04dce93-57f6-492f-aa54-5f037aaf943f"
/>

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->
- In the new behavior, the corresponding CSS was moved in to the
`textarea.native.scss` file that is inherited by both ios and md themes,
leaving ionic theme unaffected.
- After the change:
<img width="457" height="174" alt="image"
src="https://github.com/user-attachments/assets/ef9cbb22-b5d2-4845-a01d-e0540fe1df70"
/>

## Does this introduce a breaking change?
- [ ] Yes
- [x] No

<!--
  If this introduces a breaking change:
1. Describe the impact and migration path for existing applications
below.
  2. Update the BREAKING.md file with the breaking change.
3. Add "BREAKING CHANGE: [...]" to the commit description when merging.
See
https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#footer
for more information.
-->


## Other information

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

---------

Co-authored-by: ionitron <hi@ionicframework.com>

core/src/components/textarea/textarea.common.scss

@@ -506,17 +506,6 @@
   z-index: 2;
 }
 
-/**
- * Ensures the textarea does not
- * overlap the label.
- */
-:host(.textarea-label-placement-stacked) textarea,
-:host(.textarea-label-placement-floating) textarea,
-:host(.textarea-label-placement-stacked[auto-grow]) .native-wrapper::after,
-:host(.textarea-label-placement-floating[auto-grow]) .native-wrapper::after {
-  @include margin(8px, 0px, 0px, 0px);
-}
-
 /**
  * This makes the label sit over the textarea
  * when the textarea is blurred and has no value.

core/src/components/textarea/textarea.native.scss

@@ -120,6 +120,20 @@
   @include globals.margin(0, globals.$form-control-label-margin, 0, 0);
 }
 
+// Textarea Label Placement - Stacked & Floating
+// ----------------------------------------------------------------
+
+/**
+ * Ensures the textarea does not
+ * overlap the label.
+ */
+:host(.textarea-label-placement-stacked) textarea,
+:host(.textarea-label-placement-floating) textarea,
+:host(.textarea-label-placement-stacked[auto-grow]) .native-wrapper::after,
+:host(.textarea-label-placement-floating[auto-grow]) .native-wrapper::after {
+  @include globals.margin(8px, 0px, 0px, 0px);
+}
+
 // Start / End Slots
 // ----------------------------------------------------------------