Expose two customizations for `TextField` on Android

[boctor]

• Specify a VisualTransformation for changing the visual output of the text
• Specify an onValueChange closure to process the textfield's text as it changes

If these customizations aren't provided, then the previous behavior is maintained:

• For VisualTransformation, PasswordVisualTransformation is used when isSecure otherwise VisualTransformation.None is used
• For onValueChange, the text binding is set to the new text value without change

Example usage:

    let textField = TextField("My TextField", text: $text)
    #if SKIP
    textField.visualTransformation = MyCustomVisualTransformation()
    textField.onValueChange = { newValue in
      text.wrappedValue = updateText(newValue)
    }
    #endif

Skip Pull Request Checklist:

• [x] REQUIRED: I have signed the Contributor Agreement
• [x] REQUIRED: I have tested my change locally with swift test
• [x] OPTIONAL: I have tested my change on an iOS simulator or device
• [x] OPTIONAL: I have tested my change on an Android emulator or device

[aabewhite]

Thanks! I'm curious about the motivation here. What are you using the visual transformation for, and how are you accomplishing the same on the iOS side? And why the onChange block rather than using SwiftUI's own onChange modifier?

I think we're close to landing on a more comprehensive way of doing Android-specific component customization. So I'll be honest that I don't think we'll use this patch, but seeing what you need and understanding the motivations is definitely helping shape the API we're coming up with.

[boctor]

Closing since these customizations are now possible with the Material 3 component customization API in #70