Create ruff_notebook crate (#7039)

## Summary

This PR moves `ruff/jupyter` into its own `ruff_notebook` crate. Beyond
the move itself, there were a few challenges:

1. `ruff_notebook` relies on the source map abstraction. I've moved the
source map into `ruff_diagnostics`, since it doesn't have any
dependencies on its own and is used alongside diagnostics.
2. `ruff_notebook` has a couple tests for end-to-end linting and
autofixing. I had to leave these tests in `ruff` itself.
3. We had code in `ruff/jupyter` that relied on Python lexing, in order
to provide a more targeted error message in the event that a user saves
a `.py` file with a `.ipynb` extension. I removed this in order to avoid
a dependency on the parser, it felt like it wasn't worth retaining just
for that dependency.

## Test Plan

`cargo test`

crates/ruff_dev/src/round_trip.rs

@@ -6,7 +6,6 @@ use std::path::PathBuf;
 
 use anyhow::Result;
 
-use ruff::jupyter;
 use ruff_python_codegen::round_trip;
 use ruff_python_stdlib::path::is_jupyter_notebook;
 
@@ -20,7 +19,7 @@ pub(crate) struct Args {
 pub(crate) fn main(args: &Args) -> Result<()> {
     let path = args.file.as_path();
     if is_jupyter_notebook(path) {
-        println!("{}", jupyter::round_trip(path)?);
+        println!("{}", ruff_notebook::round_trip(path)?);
     } else {
         let contents = fs::read_to_string(&args.file)?;
         println!("{}", round_trip(&contents, &args.file.to_string_lossy())?);