add new Literal API for pure literal expressions:

Design compile time api hs_compile_lit() and hs_compile_lit_multi()
to handle pure literal pattern sets. Corresponding option --literal-on
is added for hyperscan testing suites. Extended parameters and part of
flags are not supported for this api.

src/parser/shortcut_literal.cpp

@@ -185,7 +185,6 @@ bool shortcutLiteral(NG &ng, const ParsedExpression &pe) {
         return false;
     }
 
-    vis.lit.set_pure();
     const ue2_literal &lit = vis.lit;
 
     if (lit.empty()) {