feat: expose Android ML Kit scanner mode

[BhavyaJain711]

Summary

Expose Google ML Kit document scanner modes to JavaScript on Android.

Changes

• Added ScannerMode constants:

  • ScannerMode.BASE
  • ScannerMode.BASE_WITH_FILTER
  • ScannerMode.FULL

• Added optional scannerMode to ScanDocumentOptions.

• Explicitly mapped supported scanner modes in the Android native module.

• Preserved FULL as the default for backwards compatibility.

• Added a safe fallback to FULL for invalid native input.

• Updated the README with API documentation and usage examples.

• Added a scanner-mode selector to the Android example app for manual testing.

• Added tests for the exported scanner-mode constants.

Example

import DocumentScanner, {
  ScannerMode,
} from 'react-native-document-scanner-plugin';

const { scannedImages } = await DocumentScanner.scanDocument({
  scannerMode: ScannerMode.BASE,
});

Testing

• TypeScript typecheck: passed
• Jest tests: passed
• Lint: passed with one existing unrelated warning
• Package build: passed
• Pre-commit hooks: passed
• Android emulator/device testing: passed

FULL remains the default, and iOS behavior is unchanged.