DiscordEmbedBuilder doesn't handle URL-encoded spaces properly in some fields

Created by: xSke

When passing an URL containing URL-encoded spaces (%20) to some EmbedBuilder methods (specifically, WithAuthor's url and iconUrl parameters and WithFooter's iconUrl parameter), this will cause a 400 Bad Request on Discord's end when sending said embed. Embed images and thumbnails work fine with the same URL, though.

An example of an URL that triggers this: https://via.placeholder.com/728x90.png?text=Hello%20World

As far as I can tell, this is because DiscordEmbedBuilder.Build() re-wraps these fields into a new Uri/DiscordUri instance by going through DiscordEmbedAuthor/DiscordEmbedFooter's property getters, calling .ToString(), which gets rid of the URL encoding and doesn't pass it on. This is visible in the resulting exception's WebRequest payload:

{
    "tts": false,
    "embed": {
        "thumbnail": {
            "url": "https://via.placeholder.com/728x90.png?text=Hello%20World",
            "height": 0,
            "width": 0
        },
        "author": {
            "name": "Foobar",
            "icon_url": "https://via.placeholder.com/728x90.png?text=Hello World"
        }
    }
}

And the resulting response:

{"code": 50035, "errors": {"embed": {"author": {"icon_url": {"_errors": [{"code": "URL_TYPE_INVALID_URL", "message": "Not a well formed URL."}]}}}}, "message": "Invalid Form Body"}

embed.thumbnail.url has the URL-encoding passed through correctly, while embed.author.icon_url doesn't.