Correctly support backtick-enclosed strings

See https://www.php.net/manual/en/language.operators.execution.php
and https://wiki.php.net/rfc/deprecate-backtick-operator

Author: thekid

src/main/php/lang/ast/Tokens.class.php

@@ -10,7 +10,7 @@
  * @test  lang.ast.unittest.TokensTest
  */
 class Tokens {
-  const DELIMITERS = " \r\n\t'\$\"=,;.:?!(){}[]#+-*/|&^@%~<>";
+  const DELIMITERS = " \r\n\t'\$\"`=,;.:?!(){}[]#+-*/|&^@%~<>";
   const OPERATORS = [
     '<' => ['<=>', '<<=', '<=', '<<', '<>', '<?'],
     '>' => ['>>=', '>=', '>>'],
@@ -101,7 +101,7 @@ public function iterator($language) {
         $line++;
       } else if ("\r" === $token || "\t" === $token || ' ' === $token) {
         // Skip over whitespace
-      } else if ("'" === $token || '"' === $token) {
+      } else if ("'" === $token || '"' === $token || '`' === $token) {
         $string= $token;
         $end= '\\'.$token;
         do {

src/test/php/lang/ast/unittest/parse/LiteralsTest.class.php

@@ -50,6 +50,11 @@ public function non_empty_string() {
     $this->assertParsed([new Literal('"Test"', self::LINE)], '"Test";');
   }
 
+  #[Test]
+  public function exec_statement() {
+    $this->assertParsed([new Literal('`ls -al`', self::LINE)], '`ls -al`;');
+  }
+
   #[Test, Values(['[];', ['array();']])]
   public function empty_array($declaration) {
     $this->assertParsed([new ArrayLiteral([], self::LINE)], $declaration);