fix(android): uses unique authorities for file provider

[huextrat]

Summary

• Use a library-specific FileProvider subclass (StripeFileProvider) in the Android manifest instead of the generic androidx.core.content.FileProvider. Giving this library's provider a unique android:name prevents the manifest merger from merging it with another library's FileProvider, which would cause an "Attribute provider@authorities value=... is also present at..." conflict.
• Authority remains ${applicationId}.fileprovider; no changes to StripeSdkModule.kt or CSV export sharing.

fixes: #2307

Motivation

When an app uses both @stripe/stripe-react-native and another library that declares a FileProvider (e.g. for document viewing), the Android manifest merger can report a conflict on the android:authorities attribute because both components use the same FileProvider class and similar or competing authorities. Using a dedicated subclass (StripeFileProvider) gives this library's provider a distinct android:name, so the merger keeps it separate and the conflict is resolved without requiring app-level tools:replace workarounds.

Testing

• I tested this manually
• I added automated tests

Documentation

Select one:

• I have added relevant documentation for my changes.
• This PR does not result in any developer-facing changes.

[huextrat]

FileProvider was added by @gimenete-stripe with #2298