Secure PDF Viewer

Notable changes in version 20:

• improve app compatibility by trying to load data with no MIME type passed
• improve zoom gesture by scrolling during zooming to keep focus in the same place instead of the top left corner
• hide text layer during scaling to avoid scrollable blank space when zooming out
• update dependencies
• update target SDK to 35 (Android 15)
• enable generation of v4 APK signatures

See https://github.com/GrapheneOS/PdfViewer/releases/tag/20 for the full release notes.