Placeholders for .po source to .xml and .strings files

### Describe the issue

Hello, our translation files in Weblate are based in .po and they are the base for translating to Android .xml and iOS .strings. We have configured `$STRING$` for string placeholder, as in the screenshot below

When exporting to Android .xml we want the `$STRING$` to be converted to `%s` while exporting to iOS .strings, we want the `
$STRING$` to be converted to `%@`. Is there a way to make this happen without having two different translation projects/components, one for Android, and the other one for iOS?

### I already tried

- [X] I've read and searched [the documentation](https://docs.weblate.org/).
- [X] I've searched for similar issues in this repository.

### Steps to reproduce the behavior

Configure any placeholders in the settings

### Expected behavior

When exporting to Android .xml we want the `$STRING$` to be converted to `%s` while exporting to iOS .strings, we want the `
$STRING$` to be converted to `%@`. Is there a way to make this happen without having two different translation projects/components, one for Android, and the other one for iOS?

### Screenshots

_No response_

### Exception traceback

_No response_

### How do you run Weblate?

Docker container

### Weblate versions

_No response_

### Weblate deploy checks

_No response_

### Additional context

_No response_