[#61826] Add blob() method to DotNetStreamReference

[andersabjorn]

Add blob() method to DotNetStreamReference

Description

This PR implements the blob() method for DotNetStreamReference as requested in issue #61826.

Changes Made:

• Add async blob(mimeType?: string): Promise<Blob> method to DotNetStream class in Microsoft.JSInterop.ts
• Update JavaScript interop tests in jsinteroptests.js to validate blob functionality
• Method allows optional MIME type parameter for content-type headers
• Follows the same pattern as existing arrayBuffer() method

Usage Example:

// Get stream data as a Blob
const blob = await dotNetStreamRef.blob('application/pdf');

// Create download link
const url = URL.createObjectURL(blob);
const a = document.createElement('a');
a.href = url;
a.download = 'document.pdf';
a.click();

// Display image
const img = document.createElement('img');
img.src = URL.createObjectURL(blob);

Fixes #61826

[dotnet-policy-service]

Thanks for your PR, @andersabjorn. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[andersabjorn]

@dotnet-policy-service agree