LibJS: Implement basic lexing + parsing of StringLiteral

This still includes the double-quote characters (") but at least the
AST comes out right.

Libraries/LibJS/Lexer.cpp

@@ -195,6 +195,13 @@ Token Lexer::next()
             consume();
         }
         token_type = TokenType::NumericLiteral;
+    } else if (m_current_char == '"') {
+        consume();
+        while (m_current_char != '"') {
+            consume();
+        }
+        consume();
+        token_type = TokenType::StringLiteral;
     } else if (m_current_char == EOF) {
         token_type = TokenType::Eof;
     } else {

Libraries/LibJS/Parser.cpp

@@ -89,6 +89,8 @@ NonnullOwnPtr<Expression> Parser::parse_primary_expression()
         return make<NumericLiteral>(consume().double_value());
     case TokenType::BoolLiteral:
         return make<BooleanLiteral>(consume().bool_value());
+    case TokenType::StringLiteral:
+        return make<StringLiteral>(consume().string_value());
     case TokenType::CurlyOpen:
         return parse_object_expression();
     default: