Add multiline string length tests.

Author: Y-Less

source/compiler/tests/multiline_string_sizes.meta

@@ -0,0 +1,5 @@
+{
+  'test_type': 'output_check',
+  'errors': """
+  """
+}

source/compiler/tests/multiline_string_sizes.pwn

@@ -0,0 +1,23 @@
+// This file should pass with \r\n and \n.
+
+new str1[] = "hello";
+#assert sizeof(str1) == 6
+
+new str2[] = "hello\
+";
+#assert sizeof(str2) == 6
+
+new str3[] = "hello\
+           ";
+#assert sizeof(str3) == 6
+
+new str4[] = "hello\
+           world";
+#assert sizeof(str4) == 11
+
+new str5[] = "hello
+           world";
+#assert sizeof(str5) == 23
+
+#pragma unused str1, str2, str3, str4, str5
+