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/back-button/back-button.tsx

@@ -62,6 +62,7 @@ export class BackButton implements ComponentInterface {
     return {
       class: {
         ...createColorClasses(this.color),
+        [`${this.mode}`]: true,
 
         'button': true, // ion-buttons target .button
         'ion-activatable': true,