Attachment protocol URLs should support name conversion

[MinnDevelopment]

When you upload a file named hello (world).png, it will be renamed to hello_world.png. The attachment://filename.png used in embeds is not changed, which results in a resolution failure and the image is not added to the embed.
Maybe this same rename strategy could also be performed on the link to make this compatible?

This was originally brought up in #4292, which documented the behavior. However, this should probably be addressed and improved for a better user experience. @IanMitchell asked me to open a discussion for this problem.