fix(input): string values are emitted (#27226)

Issue number: N/A

---------

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

The `InputChangeEventDetail` and `InputInputEventDetail` interfaces were
updated to add a number type to the value key:
https://github.com/ionic-team/ionic-framework/pull/26176

This was done to align with the value property on ion-input which allows
for strings and numbers. However, this is incorrect as the value emitted
is always forced to a string:
c9bddbdb4c/core/src/components/input/input.tsx (L416)


We likely copied the the type definition for the `value` prop not
realizing that number values are never emitted.

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

- The `InputChangeEventDetail` and `InputInputEventDetail` interfaces no
longer have the `number` type
- The value passed to `ionInput` is converted to a string. (This isn't
really needed since the native `<input>` element will have a type of
string when the user types, but I added it for consistency with the
`ionChange` emission).
- Added a code comment to highlight this behavior

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

Note: This is not a breaking change because `number` values were never
emitted in the first place.

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## Other information

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

core/src/components/input/input-interface.ts

@@ -1,12 +1,17 @@
+/**
+ * Values are converted to strings when emitted which is
+ * why we do not have a `number` type here even though the
+ * `value` prop accepts a `number` type.
+ */
 export interface InputChangeEventDetail {
-  value?: string | number | null;
+  value?: string | null;
   event?: Event;
 }
 
 // We recognize that InputInput is not an ideal naming pattern for this type.
 // TODO (FW-2199): Explore renaming this type to something more appropriate.
 export interface InputInputEventDetail {
-  value?: string | number | null;
+  value?: string | null;
   event?: Event;
 }
 

core/src/components/input/input.tsx

@@ -424,7 +424,11 @@ export class Input implements ComponentInterface {
    */
   private emitInputChange(event?: Event) {
     const { value } = this;
-    this.ionInput.emit({ value, event });
+
+    // Checks for both null and undefined values
+    const newValue = value == null ? value : value.toString();
+
+    this.ionInput.emit({ value: newValue, event });
   }
 
   private shouldClearOnEdit() {