[Request]: package_info_plus needs to give SHA1, not just SHA256

### Plugin

package_info_plus

### Use case

Right now the `packageInfo.buildSignature` method returns a SHA256 hex string (without colon byte delimiters).

The Android ecosystem still extensively uses SHA1 hex strings (with colon byte delimeters), and sometimes SHA1, base64-encoded.

`package_info_plus` really needs to provide this information in more formats.

### Proposal

For inspiration, please see the options available in https://pub.dev/packages/package_signature .

I'd rather not have to pull in that other package, which duplicates work of `package_info_plus` (which I already need).

Inizia leggendo l’implementazione di packageInfo.buildSignature in package_info_plus e confronta i formati di output disponibili in package_signature. Il lavoro è concluso quando package_info_plus espone lo SHA1 esadecimale con delimitatori di due punti e la forma base64, insieme al valore SHA256 esistente.

Scritto dal modello di indicizzazione a partire dal testo della issue.