feat(input, textarea, select): add start and end slots (#28583)

Issue number: Resolves #26297

---------

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issue. -->

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etc). Submit multiple pull requests if needed. -->

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

With the modern form control syntax, it is not possible to add icon
buttons or other decorators to the sides of `ion-input`, `ion-textarea`,
or `ion-select`, as you can with `ion-item`.

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

`start` and `end` slots added to each component.

This PR is a combination of several others that were already approved.
If needed, it might be easiest to review the PRs individually by looking
at the commit history here.

## 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. -->

Docs PR: https://github.com/ionic-team/ionic-docs/pull/3271

Dev build: `7.5.4-dev.11701112913.1ea61220`

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

core/src/components/input/input.tsx

@@ -26,6 +26,8 @@ import { getCounterText } from './input.utils';
  * @virtualProp {"ios" | "md"} mode - The mode determines which platform styles to use.
  *
  * @slot label - The label text to associate with the input. Use the `labelPlacement` property to control where the label is placed relative to the input. Use this if you need to render a label with custom HTML. (EXPERIMENTAL)
+ * @slot start - Content to display at the leading edge of the input. (EXPERIMENTAL)
+ * @slot end - Content to display at the trailing edge of the input. (EXPERIMENTAL)
  */
 @Component({
   tag: 'ion-input',
@@ -369,7 +371,7 @@ export class Input implements ComponentInterface {
     const { el } = this;
 
     this.legacyFormController = createLegacyFormController(el);
-    this.slotMutationController = createSlotMutationController(el, 'label', () => forceUpdate(this));
+    this.slotMutationController = createSlotMutationController(el, ['label', 'start', 'end'], () => forceUpdate(this));
     this.notchController = createNotchController(
       el,
       () => this.notchSpacerEl,
@@ -697,18 +699,42 @@ export class Input implements ComponentInterface {
   }
 
   private renderInput() {
-    const { disabled, fill, readonly, shape, inputId, labelPlacement } = this;
+    const { disabled, fill, readonly, shape, inputId, labelPlacement, el, hasFocus } = this;
     const mode = getIonMode(this);
     const value = this.getValue();
     const inItem = hostContext('ion-item', this.el);
     const shouldRenderHighlight = mode === 'md' && fill !== 'outline' && !inItem;
 
+    const hasValue = this.hasValue();
+    const hasStartEndSlots = el.querySelector('[slot="start"], [slot="end"]') !== null;
+
+    /**
+     * If the label is stacked, it should always sit above the input.
+     * For floating labels, the label should move above the input if
+     * the input has a value, is focused, or has anything in either
+     * the start or end slot.
+     *
+     * If there is content in the start slot, the label would overlap
+     * it if not forced to float. This is also applied to the end slot
+     * because with the default or solid fills, the input is not
+     * vertically centered in the container, but the label is. This
+     * causes the slots and label to appear vertically offset from each
+     * other when the label isn't floating above the input. This doesn't
+     * apply to the outline fill, but this was not accounted for to keep
+     * things consistent.
+     *
+     * TODO(FW-5592): Remove hasStartEndSlots condition
+     */
+    const labelShouldFloat =
+      labelPlacement === 'stacked' || (labelPlacement === 'floating' && (hasValue || hasFocus || hasStartEndSlots));
+
     return (
       <Host
         class={createColorClasses(this.color, {
           [mode]: true,
-          'has-value': this.hasValue(),
-          'has-focus': this.hasFocus,
+          'has-value': hasValue,
+          'has-focus': hasFocus,
+          'label-floating': labelShouldFloat,
           [`input-fill-${fill}`]: fill !== undefined,
           [`input-shape-${shape}`]: shape !== undefined,
           [`input-label-placement-${labelPlacement}`]: true,
@@ -717,9 +743,16 @@ export class Input implements ComponentInterface {
           'input-disabled': disabled,
         })}
       >
-        <label class="input-wrapper">
+        {/**
+         * htmlFor is needed so that clicking the label always focuses
+         * the input. Otherwise, if the start slot has something
+         * interactable, clicking the label would focus that instead
+         * since it comes before the input in the DOM.
+         */}
+        <label class="input-wrapper" htmlFor={inputId}>
           {this.renderLabelContainer()}
           <div class="native-wrapper">
+            <slot name="start"></slot>
             <input
               class="native-input"
               ref={(input) => (this.nativeInput = input)}
@@ -774,6 +807,7 @@ export class Input implements ComponentInterface {
                 <ion-icon aria-hidden="true" icon={mode === 'ios' ? closeCircle : closeSharp}></ion-icon>
               </button>
             )}
+            <slot name="end"></slot>
           </div>
           {shouldRenderHighlight && <div class="input-highlight"></div>}
         </label>