unescape backslash-doublequote for DSL string literals

c/dsls/mlr_dsl_parse.y

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <math.h>
+#include "../lib/mlrutil.h"
 #include "../containers/mlr_dsl_ast.h"
 #include "../containers/sllv.h"
 
@@ -800,7 +801,7 @@ md_string(A) ::= MD_TOKEN_STRING(B). {
 	char* stripped = &input[1];
 	int len = strlen(input);
 	stripped[len-2] = 0;
-	A = mlr_dsl_ast_node_alloc(stripped, B->type);
+	A = mlr_dsl_ast_node_alloc(mlr_unbackslash(stripped), B->type);
 }
 md_regexi(A) ::= MD_TOKEN_REGEXI(B). {
 	char* input = B->text;

c/reg_test/expected/out

@@ -11019,7 +11019,7 @@ AST BEGIN STATEMENTS (0):
 AST MAIN STATEMENTS (1):
 =~ (operator):
     y (field_name).
-    \".. (strnum_literal).
+    ".. (strnum_literal).
 AST END STATEMENTS (0):
 x=ABCDE,y="GHI"
 

c/todo.txt

@@ -10,6 +10,7 @@ TOP-OF-LIST SUMMARY
 * rh/fedora/centos mlr-3.4.0
 
 * \" in string-literal reader ... fix up in the parser or in rval_expr.
+* basenaming syntax for subselector emits
 ~ oosvar-to-oosvar assignments with treecopy
 ~ subselector emits
 ~ horizontality of emits