Add ability to create a report per-target/extension

[edorphy]

Hey Paul,

Similar to #39, I'm curious on your take of how easy it would be to modify SitRep to allow the caller to specify a flag to output a report per target, per extension, etc.

For example, 'I have an app with an app, app clip, widget extension, live activity widget extension' and so on. The idea here would be to see at a glance where the majority of the code is from a target level. Potentially some interesting analysis to 'refactor shared code into swift package'.

[twostraws]

As long as the target/extension were in a clearly marked group, this wouldn't be tricky at all. I'm not sure whether this would mean querying the Xcode project file or not, but if it did… 💀 (I think! Maybe there are smart, modern ways of doing this.)