docs(stencil): add stencil usage to components (#21261)

core/src/components/icon/usage/stencil.md

@@ -0,0 +1,26 @@
+```tsx
+import { Component, h } from '@stencil/core';
+
+@Component({
+  tag: 'icon-example',
+  styleUrl: 'icon-example.css'
+})
+export class IconExample {
+  render() {
+    return [
+      // uses "star" icon for both modes
+      <ion-icon name="star"></ion-icon>,
+
+      // explicitly set the icon for each mode
+      <ion-icon ios="home" md="star"></ion-icon>,
+
+      // use a custom svg icon
+      <ion-icon src="/path/to/external/file.svg"></ion-icon>,
+
+      // set the icon size
+      <ion-icon size="small" name="heart"></ion-icon>,
+      <ion-icon size="large" name="heart"></ion-icon>
+    ];
+  }
+}
+```