Expand video attached image extraction to support multiple images/types

[1337joe]

Changes

• Split VideoImageProvider to create EmbeddedImageProvider: Video for taking a screenshot of a video, Embedded for extracting image attachments.
• Expanded EmbeddedImageProvider to support multiple embedded image types in the same file: Primary, Background, Logo
• Added support for changing the extension of extracted images to match the type of the embedded image (important for embedded pngs with transparency, which can't be rendered to jpg).
• Added tests for VideoImageProvider and EmbeddedImageProvider

Rationale

• I have movies with the cover embedded and I want to prioritize that over online providers, but I don't want a screenshot from the movie if any other image is available. To match my desired priority order (Embedded > Online > Screenshot) I had to split attachment extraction out of VideoImageProvider into a separate provider. To minimize disruption the default order is for the new embedded provider to come just before the old one, which matches the behavior of the old combined provider.
• Multiple images and file types can be embedded in an mkv video file, so I added checking against the filename/mimetype to determine the type of image and extension so the basic movie image types (poster, background, logo) can be embedded in a movie file.

[1337joe]

Attached images in mkv files are currently parsed as MediaStreams with MediaStreamType.EmbeddedImage (see line 738 of this file). To determine the type of an attached image I needed the filename and/or mimetype fields, which are only stored for MediaAttachments.

This was the minimal change to store the available metadata in the current structures, but it results in storing attached images in both the MediaAttachment and MediaStream lists. If there is a better way to store the data I'm open to suggestions.

[cvium]

I think I would put this in ExtractImageInternal and rewrite it as this

            if (string.IsNullOrEmpty(outputExtension))
            {
                outputExtension = ".jpg";
            }
            else if (outputExtension[0] != '.')
            {
                outputExtension = "." + outputExtension;
            }

[1337joe]

Sorry for the slow response, was away for the weekend without electronics.

Rider underlined it when I reassigned a parameter so I thought that was discouraged. I prefer this pattern as well, and I forget why I put it one method earlier in the call chain.

If this completes what you want changed let me know and I'd be happy to squash the review comment commits to clean up the git log.

[cvium]

Rider underlined it when I reassigned a parameter so I thought that was discouraged. I prefer this pattern as well, and I forget why I put it one method earlier in the call chain.

I get why it underlines it. It's not nice, but in this case I think a new variable is overkill.

If this completes what you want changed let me know and I'd be happy to squash the review comment commits to clean up the git log.

I don't particularly care, but if you want to squash it, the go ahead (and I see you did).