Add API for annotation processing

[radazzouz]

Details

Came up in Z#17532

Usage

// First, save all annotations in the current document.
this.refs.pdfView.saveCurrentDocument().then(success => {
  if (success) {
    // Then, flatten all the annotations
    PSPDFKit.processAnnotations(
      "flatten",
      "all",
      sourceDocumentPath,
      processedDocumentPath
    )
      .then(success => {
        if (success) {
          // And finally, present the newly processed document with flattened annotations.
          PSPDFKit.present(processedDocumentPath, {});
        } else {
          alert("Failed to embed annotations.");
        }
      })
      .catch(error => {
        alert(JSON.stringify(error));
      });
  } else {
    alert("Failed to save current document.");
  }
});

Acceptance Criteria

• Add javascript API for annotation processing on Android.
• Add javascript API for annotation processing on iOS.
• When approved, right before merging, rebase with master and increment the package version in package.json, package-lock.json, samples/Catalog/package.json, and samples/NativeCatalog/package.json (see example commit: 1bf805f).
• Create a new release (and tag) with the new package version (see https://github.com/PSPDFKit/react-native/releases).

[irgendeinich]

iOS JS part looks good to me.

[steviki]

iOS ObjC and JS parts look good to me. 👍

[simoarpe]

Android part looks good