Introduce a stable line ID that continues to increment after being trimmed

[Tyriar]

Some things we're looking at adding in VS Code are references to arbitrary ranges in the buffer like selection and command and would like some identifier that makes sense to both the UI and in the VS Code extension API. Here's a look at what file references look like to the user in Copilot:

I was thinking for terminal it would look similar, something like:

pwsh:123-103 PS C:....
(terminal title):(start line)-(end line) (preview of text)

We have markers but these are done in a way such that they don't track a stable line but instead continue to update. This refactor would also allow us to not update marker lines on every trim which would be a win for perf, especially when the embedder uses a lot of markers (like VS Code).