fix(components): include mode classes on components for use in shadow (#17838)

- removes mode-less component classes from the internal CSS, use element instead
- adds mode specific classes `md` or `ios` for styling inside of shadow components
- adds e2e test that verifies mode classes exist on all ionic components, plus checks for specific classes that the components need for internal styling

fixes #17608

core/src/components/thumbnail/thumbnail.tsx

@@ -1,11 +1,22 @@
 import { Component, ComponentInterface } from '@stencil/core';
 
+import { Mode } from '../../interface';
+
 @Component({
   tag: 'ion-thumbnail',
   styleUrl: 'thumbnail.scss',
   shadow: true
 })
 export class Thumbnail implements ComponentInterface {
+  mode!: Mode;
+
+  hostData() {
+    return {
+      class: {
+        [`${this.mode}`]: true,
+      }
+    };
+  }
   render() {
     return <slot></slot>;
   }