Fix handling of status changes by git plugin when file content changes

[jeremypw]

Partially fixes #2261

• Fix how git plugin handles update_file_info - update git status for single file
• Emblem on new files in working directory as well as index
• Ensure update_file_info is called for file changes
• Ensure update_file_info called for file-added events even if file already in cache
• Ignore transient outputstream files so they do not trigger calls to update_file_info

[danirabbit]

@jeremypw can you resolve conflicts here?

[jeremypw]

Linked issue not fixed after merging main - investigating.

[jeremypw]

So, it looks like this never solved the entire issue. It only solves the case where the file content changes, so the emblem will change to "modified" when there are uncommitted changes and is removed if the uncommitted changes are reverted. New untracked files will get the appropriate emblem when they appear.

However, the emblem does not change automatically when there is a commit made. This is because the file itself does not change - it is the git database that changes. The Code application does detect this because it monitors the .git folder of the active project. It would add significant complication to Files to do this as it is not project-centric. It may be necessary to promote the git plugin to main code like in Code.

Not sure if this partial fix is still worth merging or whether to try for a full fix.

[jeremypw]

Closing as not complete fix and no reviews