feat: nicer string interpolation

src/rules/string.rs

@@ -141,9 +141,11 @@ pub fn rule(
                     ));
 
                     if index + 1 != portions.len() {
+                        steps.push_back(crate::builder::Step::Indent);
                         steps.push_back(crate::builder::Step::FormatWider(
                             interpolations.next().unwrap().clone(),
                         ));
+                        steps.push_back(crate::builder::Step::Dedent);
                     }
                 }
             }

tests/cases/string/in

@@ -78,4 +78,14 @@
         <plist version="1.0">
         ${ expr "" v }
         </plist>''
+
+  ''
+    --${
+    "test"
+  }
+  ''
+
+  "--${
+    "test"
+  }"
 ]

tests/cases/string/out

@@ -78,4 +78,14 @@
     <plist version="1.0">
     ${expr "" v}
     </plist>''
+
+  ''
+    --${
+      "test"
+    }
+  ''
+
+  "--${
+    "test"
+  }"
 ]