feat: Include canvas files when determining orphans

[MostlyArmless]

Main change

Mainly, this change is to close issue #43:

1. We've already loaded a list of all vault files, so filter out just the .canvas files
2. loop over the canvas files, load their contents, parse the JSON and find any links to other files. That set of links is the same one that we're already populating when iterating all the markdown files.
3. Now, when we check if a file is orphaned, this plugin will no longer consider a file to be orphaned if it exists in or is linked to from exclusively .canvas files.

I smoke tested this briefly on my vault and didn't see any issues.

Other small changes

This change includes a few small performance improvements:

• using a Set instead of an array for O(1) membership checks
• only checking for the outFile until it's been found once

Some clarity improvements:

• Renamed variables/methods to be more self-explanatory

[MostlyArmless]

Apologies for the messy diff, I think my IDE applied some whitespace adjustments I didn't realize. If you view the diffs in VS Code it should be easier to read.

[Vinzent03]

Thanks for your contribution! I needed some time and fixed/changed some things, but this is now ready to go. :tada: