Introduce blob handling for Android & iOS

[riderx]

Summary

This PR introduces blob handling for Android & iOS webviews, based on the work from PR #5498 and updated to work with the latest main branch.

Whenever a blob:/ URL or normal download is requested to be 'opened', a folder selection is prompted and the file is saved.

This addresses issue #5478

Features

• Base64 blobs through blob:data... scheme - Handles both known and unknown mime-types
  • Both Android and iOS were opening images (like PNG) in the internal browser, causing users to be stuck on the image requiring manual app closure
• Blob links through blob:http... scheme
• Web worker initiated downloads - Partially addressed (browser core limitations may apply)

Implementation Details

iOS

• Works on iOS 14.5+ (WebKit exposed necessary APIs starting from this version)
• When a download request is received, prompts for folder selection and saves the file with a unique filename
• Includes compiler guards for Xcode 12 compatibility

Android

• Implements JS interface that injects JS code to download the received URL through XHR
• Uses the JS accessible context to pipe content in chunks to an Intent for file selection
• Implements duplex stream for piping received content to file

Common

• Both platforms ask users for destination selection
• Implement download notifications to be consumed by App plugin
• Applications can decide what to do with notifications (show alert, display in list, etc.)

Test Cases

Test cases are available at: https://github.com/ikon-integration/Capacitor-Blob-Download-Issue

Changes from original PR #5498

• Resolved all merge conflicts with current main branch
• Maintained compatibility with existing code structure
• Preserved all bug fixes and improvements from the original PR