Fix an issue where we weren't properly escaping backslashes in quoted strings when converting to the DSL.

Author: DaveEwing

Sources/_StringProcessing/PrintAsPattern.swift

@@ -578,7 +578,7 @@ extension PrettyPrinter {
 extension String {
   // TODO: Escaping?
   fileprivate var _quoted: String {
-    "\"\(self._replacing("\"", with: "\\\""))\""
+    "\"\(self._replacing("\\", with: "\\\\")._replacing("\"", with: "\\\""))\""
   }
 }
 

Tests/RegexTests/RenderDSLTests.swift

@@ -114,4 +114,12 @@ extension RenderDSLTests {
         """)
     }
   }
+  
+  func testQuoting() throws {
+    try testConversion(#"\\\"a\""#, #"""
+      Regex {
+        "\\\"a\""
+      }
+      """#)
+  }
 }