Add a test for literal string blocks.

js/test_cases/literal_string_block/input1.json

@@ -0,0 +1 @@
+{"name": "Bob"}

js/test_cases/literal_string_block/main.dust

@@ -0,0 +1,5 @@
+{`
+This block is supposed
+    to preserve {name} all 
+newlines, whitespace, and braces
+`}