[Edge] Support for uploading images with base64 source

[f1ames]

This is a follow up #5172.

Since the File API is used during image base64 to file conversion, it doesn't work on Edge as File constructor is not supported there (see https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/9551546/).

Alternatively the Blob object could be used, however blobs itself do not provide a way to define a filename. This is problematic since during upload the filename is read from the file object and send with other data:

and with Blob instance, the filename is always set to "blob":

which doesn't work well with upload integration:

• File with the same name is always send to the server.
• File name doesn't have the extension so checking file type by extension fails.

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We need to figure out a way to provide custom filename so it can be send with upload request. It may be done by adjusting blob object so the browser uses custom name which was added (not 100% sure, my initial tests failed here). The second option is to pass filename to a loader so it is used further in the uploading process (added to formData object).

[f1ames]

During development of the main feature (#246), we have decided that all uploaded images will have image.ext name, which means that server-side implementation of the file uploading should take care of proper naming.
The only problem with Edge is that files are uploaded with blob filename - but apart from that Blob's can be uploaded the same way as File's. So maybe if we had assumed that server-side code takes care of naming, we could upload the blob files in Edge (which seems to be better solution than just removing images from pasted content) and add a proper documentation for this case for handling blob named files. WDYT? cc @Reinmar

[tomalec]

Seems the issue is solved by Edge switching to Chromium. I run automated tests and a few manual ones. Checked http://localhost:8125/ckeditor5-image/tests/manual/imageupload.html precisely.

So, from a newbie perspective seems, as solved.

[tomalec]

Closing as no longer a problem.