iOS ion-input .native-input[disabled] opacity

**Description:**

I was changing my CSS theme when I realized that in iOS for some reason the opacity is not removed in the ion-inputs.

I have my application configured in md style and I have a class for all native-input[disabled] and on android is fine but on iOS looks like it has extra non-configurable opacity which makes the letter barely readable with that tone.
Hope some help on this.
All the best.

**Steps to Reproduce:**

```
// in app.module.ts
IonicModule.forRoot({
mode: 'md'
})

// in variables.scss inside root:
.native-input[disabled] {
opacity: 1;
background-color: transparent;
color: var(--ion-color-medium); // #999999
}
```

**Output:**

**My `ionic info`:**

```

Ionic:

Ionic CLI : 6.17.1 (/usr/local/lib/node_modules/@ionic/cli)
Ionic Framework : @ionic/angular 5.8.4
@angular-devkit/build-angular : 12.1.4
@angular-devkit/schematics : 12.2.11
@angular/cli : 12.1.4
@ionic/angular-toolkit : 4.0.0

Capacitor:

Capacitor CLI : 3.2.5
@capacitor/android : 3.2.5
@capacitor/core : 3.2.5
@capacitor/ios : 3.2.4

Utility:

cordova-res : 0.15.3
native-run : 1.5.0

System:

NodeJS : v14.18.0 (/usr/local/bin/node)
npm : 7.24.2
OS : macOS Big Sur
```

**Other Information:**

Start with the app.module.ts mode configuration and the variables.scss rule for .native-input[disabled]. Reproduce the disabled ion-input appearance on iOS and compare it with Android, then inspect which Ionic styles add the opacity. Done means the intended disabled-input color and opacity are respected on iOS as well.

Escrita pelo modelo de indexação a partir do texto da issue.