fix(input, textarea, select): reduce padding on slotted buttons (#28676)

Issue number: N/A

---------

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

Buttons slotted in the start/end slots of input, textarea, or select
have a lot of excess padding that can cause them to look misaligned from
other pieces such as the control's label, especially when using
`fill="clear"`.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

Padding removed, and a border radius added so that non-clear buttons as
well as the focus state on clear buttons still look okay. Existing
screenshot tests have also been updated to include buttons (non-clear
ones so you can see the border radius in the screenshots).

Let me know if you think this should go on a feature branch instead. I
chose `main` because the current experience looks somewhat broken and we
just did a minor release recently, but this could be considered a
notable enough behavior change.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## 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>

core/src/components/input/input.ios.scss

@@ -37,3 +37,25 @@
 :host(.input-disabled) {
   opacity: #{$input-ios-disabled-opacity};
 }
+
+// Start/End Slots
+// ----------------------------------------------------------------
+
+/**
+ * Slotted buttons have a lot of default padding that can
+ * cause them to look misaligned from other pieces such
+ * as the control's label, especially when using a clear
+ * fill. We also make them circular to ensure that non-
+ * clear buttons and the focus/hover state on clear ones
+ * don't look too crowded.
+ */
+::slotted(ion-button[slot="start"].button-has-icon-only),
+::slotted(ion-button[slot="end"].button-has-icon-only) {
+  --border-radius: 50%;
+  --padding-start: 0;
+  --padding-end: 0;
+  --padding-top: 0;
+  --padding-bottom: 0;
+
+  aspect-ratio: 1;
+}