Add EXPAND-LITERAL-RANGE to Rakudo::Internals

Expands "a..e" to "abcde", "a..e..i" to "abcdefghi" and "a..ei..k"
to "abcdeijk".  Based on internal sub in Str, but now without recursion
and now also allows returning a list (with each char separately),
rather than a string

src/core/Rakudo/Internals.pm

@@ -900,6 +900,46 @@ my class Rakudo::Internals {
             !! X::Dynamic::NotFound.new(:name(name));
     }
 
+    method EXPAND-LITERAL-RANGE(Str:D \x,$list) {
+        my str $s      = nqp::unbox_s(x);
+        my int $chars  = nqp::chars($s);
+        my Mu $result := nqp::list();
+        my int $start  = 1;
+        my int $found  = nqp::index($s,'..',$start);
+
+        # found and not at the end without trail
+        while nqp::isne_i($found,-1) && nqp::isne_i($found,$chars-2) {
+
+            if $found - $start -> $unsplit {
+                nqp::splice(
+                  $result,
+                  nqp::split("",nqp::substr($s,$start - 1,$unsplit)),
+                  nqp::elems($result),
+                  0
+                )
+            }
+
+            # add the range excluding last (may be begin point next range)
+            my int $from = nqp::ordat($s,$found - 1) - 1;
+            my int $to   = nqp::ordat($s,$found + 2);
+            nqp::push($result,nqp::chr($from))
+              while nqp::islt_i($from = $from + 1,$to);
+
+            # look for next range
+            $found = nqp::index($s,'..',$start = $found + 3);
+        }
+
+        # add final bits
+        nqp::splice(
+          $result,
+          nqp::split("",nqp::substr($s,$start - 1)),
+          nqp::elems($result),
+          0
+        ) if nqp::isle_i($start,$chars);
+
+        $list ?? $result !! nqp::join("",$result)
+    }
+
     method MAKE-ABSOLUTE-PATH(Str:D $path, Str:D $abspath) {
         if $path.ord == 47 {              # 4x faster substr($path,0,1) eq "/"
             $path