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_diagnostics/src/lib.rs

@@ -1,9 +1,11 @@
 pub use diagnostic::{Diagnostic, DiagnosticKind};
 pub use edit::Edit;
 pub use fix::{Applicability, Fix, IsolationLevel};
+pub use source_map::{SourceMap, SourceMarker};
 pub use violation::{AlwaysAutofixableViolation, AutofixKind, Violation};
 
 mod diagnostic;
 mod edit;
 mod fix;
+mod source_map;
 mod violation;

crates/ruff_diagnostics/src/source_map.rs

@@ -0,0 +1,73 @@
+use ruff_text_size::{Ranged, TextSize};
+
+use crate::Edit;
+
+/// Lightweight sourcemap marker representing the source and destination
+/// position for an [`Edit`].
+#[derive(Debug, PartialEq, Eq)]
+pub struct SourceMarker {
+    /// Position of the marker in the original source.
+    source: TextSize,
+    /// Position of the marker in the transformed code.
+    dest: TextSize,
+}
+
+impl SourceMarker {
+    pub fn new(source: TextSize, dest: TextSize) -> Self {
+        Self { source, dest }
+    }
+
+    pub const fn source(&self) -> TextSize {
+        self.source
+    }
+
+    pub const fn dest(&self) -> TextSize {
+        self.dest
+    }
+}
+
+/// A collection of [`SourceMarker`].
+///
+/// Sourcemaps are used to map positions in the original source to positions in
+/// the transformed code. Here, only the boundaries of edits are tracked instead
+/// of every single character.
+#[derive(Default, PartialEq, Eq)]
+pub struct SourceMap(Vec<SourceMarker>);
+
+impl SourceMap {
+    /// Returns a slice of all the markers in the sourcemap in the order they
+    /// were added.
+    pub fn markers(&self) -> &[SourceMarker] {
+        &self.0
+    }
+
+    /// Push the start marker for an [`Edit`].
+    ///
+    /// The `output_length` is the length of the transformed string before the
+    /// edit is applied.
+    pub fn push_start_marker(&mut self, edit: &Edit, output_length: TextSize) {
+        self.0.push(SourceMarker {
+            source: edit.start(),
+            dest: output_length,
+        });
+    }
+
+    /// Push the end marker for an [`Edit`].
+    ///
+    /// The `output_length` is the length of the transformed string after the
+    /// edit has been applied.
+    pub fn push_end_marker(&mut self, edit: &Edit, output_length: TextSize) {
+        if edit.is_insertion() {
+            self.0.push(SourceMarker {
+                source: edit.start(),
+                dest: output_length,
+            });
+        } else {
+            // Deletion or replacement
+            self.0.push(SourceMarker {
+                source: edit.end(),
+                dest: output_length,
+            });
+        }
+    }
+}