fix(snap)!: Include a trailing newline in snapshots

In using snapshots, I found the leading newline so good that I feel like
we should have a trailing newline as well!

Cherry pick 7fbcc9c (assert-rs#272)

crates/snapbox/src/data/runtime.rs

@@ -143,6 +143,9 @@ fn format_patch(patch: &str) -> String {
         buf.push('\n');
     }
     buf.push_str(patch);
+    if is_multiline {
+        buf.push('\n');
+    }
     lit_kind.write_end(&mut buf).unwrap();
     if matches!(lit_kind, StrLitKind::Raw(_)) {
         buf.push(']');
@@ -359,7 +362,9 @@ mod tests {
 [r#"
 hello
 world
-"#]"##]],
+
+"#]
+"##]],
         );
 
         let patch = format_patch(r"hello\tworld");
@@ -395,6 +400,7 @@ Patchwork {
         ),
     ],
 }
+
 "#]],
         );
     }

crates/snapbox/src/data/source.rs

@@ -81,8 +81,9 @@ pub struct Inline {
 impl Inline {
     pub(crate) fn trimmed(&self) -> String {
         let mut data = self.data;
-        if data.contains('\n') && data.starts_with('\n') {
-            data = &data[1..]
+        if data.contains('\n') {
+            data = data.strip_prefix('\n').unwrap_or(data);
+            data = data.strip_suffix('\n').unwrap_or(data);
         }
         data.to_owned()
     }

crates/snapbox/tests/testsuite/assert.rs

@@ -17,6 +17,7 @@ line1
         str![[r#"
 line1
   line2
+
 "#]],
     );
 }