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/buttons/buttons.tsx

@@ -1,5 +1,7 @@
 import { Component, ComponentInterface } from '@stencil/core';
 
+import { Mode } from '../../interface';
+
 @Component({
   tag: 'ion-buttons',
   styleUrls: {
@@ -8,4 +10,14 @@ import { Component, ComponentInterface } from '@stencil/core';
   },
   scoped: true,
 })
-export class Buttons implements ComponentInterface {}
+export class Buttons implements ComponentInterface {
+  mode!: Mode;
+
+  hostData() {
+    return {
+      class: {
+        [`${this.mode}`]: true
+      }
+    };
+  }
+}