feat(input): add outline appearance for stacked label to ionic theme (#29268)

Issue number: Internal

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## What is the new behavior?
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this PR. -->

All changes are specific to the `ionic` theme.
- Styles added for `fill="outline"` plus `labelPlacement="stacked"`.
- Markup rearranged slightly to ensure label sits above outline while
still being clickable to focus the input. See code comments for details.
- The default `labelPlacement` is now `"stacked"`.
- Values for `labelPlacement` besides `"stacked"` and `"floating"`
cannot be used.

Note that per the ticket, I did not account for any other scope,
including styles for helper text, `labelPlacement="floating"`,
`shape="round"`, etc. This means that some states will look broken for
now, and will be addressed in future tickets.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

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Co-authored-by: ionitron <hi@ionicframework.com>
Co-authored-by: Maria Hutt <thetaPC@users.noreply.github.com>

core/src/components/input/input.ionic.scss

@@ -1,9 +1,14 @@
 @import "./input";
 @import "./input.ionic.vars";
+@import "./input.ionic.outline.scss";
 
 // Ionic Input
 // --------------------------------------------------
+
 :host {
+  --border-width: #{$ionic-border-size-small};
+  --border-color: #{$ionic-color-neutral-300};
+
   // TODO(FW-6113): Verify the ionic design token is correct once it's available and remove the hardcoded value.
   --highlight-color-invalid: var(--ionic-color-error-600, #970606);
 }
@@ -11,7 +16,7 @@
 // Ionic Input Sizes
 // --------------------------------------------------
 
-:host(.input-size-large) {
+:host(.input-size-large) .native-wrapper {
   min-height: 48px;
 }