feat(amazonq): support multiple uri in a single diff scheme

[ctlai95]

Problem

The current viewDiff implementation is restricted to only allowing comparing the current file contents. This means it's not possible to view a diff for a change that was applied at a previous point in time.

Solution

• Create a new DiffContentProvider that can support showing multiple URIs in the same scheme. The current ContentProvider has a limitation that it can only show a single URI.
• Refactor the code to use a defined type ViewDiffMessage instead of any
• Change the logic so that diffs are stored in memory instead of a temp file on disk

---

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• Your code changes must meet the guidelines in CONTRIBUTING.md.
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[github-actions]

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[jpinkney-aws]

isn't this basically equivalent to having a virtual file system in vscode and then adding virtual files to it?

[ctlai95]

I think yes, but I also need it to support multiple URIs to compare the before and after using the same URI scheme. I'm not sure if that part is supported by a vfs

[justinmk3]

Using a VFS is a good idea, but in this case it might not look much different in terms of new surface area (code + tests)?