mruby-compiler: replace MRB_SYM_2() with MRB_SYM() macros

The _2 suffix variants accept an mrb_state* parameter that is
always ignored with presym enabled. Replace all uses in codegen.c,
parse.y, and y.tab.c with the standard macros. The _2 macro
definitions are kept in presym headers for backward compatibility.

Co-authored-by: Claude <noreply@anthropic.com>

include/mruby/presym.h

@@ -31,8 +31,9 @@
  * excluding leading and ending punctuation.
  *
  * These macros are expanded to compile-time integer constants.
- * The `_2` suffix variants (e.g., `MRB_SYM_2`) accept an explicit
- * mruby state parameter but currently ignore it.
+ * The `_2` suffix variants (e.g., `MRB_SYM_2`) are kept for backward
+ * compatibility only; they accept an explicit `mrb_state*` parameter
+ * but ignore it. New code should use the standard macros above.
  */
 
 #endif  /* MRUBY_PRESYM_H */

include/mruby/presym/enable.h

@@ -18,6 +18,7 @@
 #define MRB_SYM_E(name) MRB_SYM_E__##name
 #define MRB_SYM(name) MRB_SYM__##name
 
+/* backward compatibility: _2 variants accept but ignore mrb_state* */
 #define MRB_OPSYM_2(mrb, name) MRB_OPSYM__##name
 #define MRB_GVSYM_2(mrb, name) MRB_GVSYM__##name
 #define MRB_CVSYM_2(mrb, name) MRB_CVSYM__##name

include/mruby/presym/scanning.h

@@ -38,6 +38,7 @@
 #define MRB_SYM_E(name) MRB_PRESYM_SCANNING_TAGGED(#name "=")
 #define MRB_SYM(name) MRB_PRESYM_SCANNING_TAGGED(#name)
 
+/* backward compatibility: _2 variants accept but ignore mrb_state* */
 #define MRB_OPSYM_2(mrb, name) MRB_OPSYM__##name(mrb)
 #define MRB_GVSYM_2(mrb, name) MRB_PRESYM_SCANNING_TAGGED("$" #name)
 #define MRB_CVSYM_2(mrb, name) MRB_PRESYM_SCANNING_TAGGED("@@" #name)