Create a native diff component

[mathewpareles]

When the user applies changes to a file, Void will highlight all of the additions in green. Here's an example:

green.diffs.mp4

However, Void should also display the parts of the file that were deleted. Here's a mock-up of what we want this to look like for the above example. The diff should include both the insertions (green) and deletions (red):

Task: Show diffs as above. This requires creating a new provider for diffs diffProvider, and using it in Void's VS Code extension.

Constraints:

1. When a diff is displayed, it should not cause a syntax error in the file.
2. When the user selects everything in the file (ctrl + a), the deletion parts of diffs should not be included in their selection.

[andrewpareles]

#119 starts this