Add blob() method to JS side of Blazor DotNetStreamReference

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Added method readableStreamToBlob() which returns a Blob from the given stream.

Description

The readableStreamToBlob method is an asynchronous function defined on the internal DotNetStream class. Its purpose is to convert a JavaScript ReadableStream (typically received from .NET interop) into a Blob URL that can be used in browser APIs (such as for downloads or displaying media).

Step-by-step Description

Obtain a Stream Reader:

The function first awaits the result of this.stream(), which returns a ReadableStream. It then calls .getReader() on this stream to obtain a reader for consuming the stream's data chunks.

Read All Chunks:

It initializes an empty array called chunks. Using a while (true) loop, it repeatedly calls reader.read(), which returns a promise resolving to an object with { done, value }.

If done is true, the stream has ended and the loop breaks.
Otherwise, it pushes the value (a chunk of data, typically a [Uint8Array]) into the [chunks] array.

Create a Blob:

After reading all chunks, it creates a new [Blob] from the collected [chunks] array. The mimeType parameter (defaulting to "application/octet-stream") is used as the Blob's type.

Create a Blob URL:

It then calls URL.createObjectURL(blob) to generate a temporary URL representing the Blob's data in memory.

Return the URL:

The function returns this Blob URL as a string. This URL can be used in browser contexts to reference the streamed data (for example, as a download link or image source).

Fixes #47685