V15: Media library crashes when uploading large files

[iOvergaard]

Description

Fixes #18012
Fixes #17493
Potentially fixes #17243

Tested in the latest Chrome:
Upload a file larger than ~50 MB and you will experience the browser tab crash.

Changes

• Allows file sizes for Kestrel and multipart forms to be a long (64-bits) as is supported by the underlying framework
• Changes from Fetch to XHR in the client to handle the large file uploads, as Chromium crashes with Fetch
• Introduces generic xhrRequest and tryXhrRequest functions for developers to call API endpoints using XHR directly
• Marks a few methods as sync (they were async before) because they were not using any awaits anywhere (could also have been a culprit of the browser crashing)

How to test

Set up Kestrel to accept files larger than 50 MB (Umbraco default). Here is how to set it to 2,5 GB:

      "Runtime": {
        "MaxRequestLength": 2097150,
        "TemporaryFileLifeTime": "0.00:30:00"
      }

• Upload a file larger than the limit and check that an error is shown both in the placeholder as well as a notification
• Upload a file larger than 50 MB (but smaller than the limit) and check that it completes
• Upload many files and check that the valid files complete
• Upload a folder with files and check that it is created as expected
• Go to Tiptap and drop an image, check it is uploaded (using the XHR request)
• Go to TinyMCE and drop an image, check it is uploaded (using the XHR request), also verify that the progress() callback works

[leekelleher]

Tested out, tried the test scenarios outlined, all looking good. 🚀

(Unsure what to do about the breaking API build errors.)