Swap quotes (#355)

- During the first iteration, we printed the unescaped values which let to printing invalid JavaScript characters and bad things like invisible characters.
- During the second iteration, we escaped everything, which generated valid JavaScript but you lost your emojis and chinese/cyrillic characters

In this iteration, which I hope will be the last one, we maintain the string exactly as encoded and only swap quotes. The swap quotes implementation is a bit convoluted but I think it works.

tests/quotes/__snapshots__/jsfmt.spec.js.snap

@@ -57,11 +57,11 @@ exports[`test strings.js 1`] = `
 \"\'\";
 
 \'\"\';
-\'\"\';
+\'\\\"\';
 \'\\\\\"\';
 
 \"\'\";
-\"\'\";
+\"\\\'\";
 \"\\\\\'\";
 
 \"\'\\\"\";
@@ -71,7 +71,7 @@ exports[`test strings.js 1`] = `
 \"\\\\\";
 
 \"\\0\";
-\"\\uD83D\\uDC36\";
+\"🐶\";
 "
 `;
 
@@ -104,11 +104,11 @@ exports[`test strings.js 2`] = `
 \"\'\";
 
 \'\"\';
-\'\"\';
+\'\\\"\';
 \'\\\\\"\';
 
 \"\'\";
-\"\'\";
+\"\\\'\";
 \"\\\\\'\";
 
 \'\\\'\"\';
@@ -118,6 +118,6 @@ exports[`test strings.js 2`] = `
 \'\\\\\';
 
 \'\\0\';
-\'\\uD83D\\uDC36\';
+\'🐶\';
 "
 `;

tests/strings/__snapshots__/jsfmt.spec.js.snap

@@ -30,17 +30,17 @@ exports[`test strings.js 1`] = `
   \"abc\",
   \"\'\",
   \'\"\',
-  \'\"\',
+  \'\\\"\',
   \'\\\\\"\',
   \"\'\",
-  \"\'\",
+  \"\\\'\",
   \"\\\\\'\",
   \"\'\\\"\",
   \"\'\\\"\",
   \"\\\\\",
   \"\\\\\",
   \"\\0\",
-  \"\\uD83D\\uDC36\",
+  \"🐶\",
   \'\\uD801\\uDC28\'
 ];
 "

tests/unicode/__snapshots__/jsfmt.spec.js.snap

@@ -73,8 +73,6 @@ function utf16Length(str, pos) {
 exports[`test keys.js 1`] = `
 "({\'この事はつもり素晴らしいことさ\': \'35jL9V\'})
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-({
-  \"\\u3053\\u306E\\u4E8B\\u306F\\u3064\\u3082\\u308A\\u7D20\\u6674\\u3089\\u3057\\u3044\\u3053\\u3068\\u3055\": \"35jL9V\"
-});
+({ \"この事はつもり素晴らしいことさ\": \"35jL9V\" });
 "
 `;