Implement direct strings. (#2196)

Direct strings are a new type of direct ecma-values (no memory allocation
is needed for encoding them) in JerryScript. Currently magic strings,
external magic strings and uint values are encoded as direct strings.

The constant pool of JerryScript byte-code is changed to hold ecma-values
rather than cpointers to support direct strings.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/parser/js/common.h

@@ -81,7 +81,7 @@ typedef struct
 {
   union
   {
-    jmem_cpointer_t value;               /**< literal value (not processed by the parser) */
+    ecma_value_t value;                  /**< literal value (not processed by the parser) */
     const uint8_t *char_p;               /**< character value */
     ecma_compiled_code_t *bytecode_p;    /**< compiled function or regexp pointer */
     uint32_t source_data;                /**< encoded source literal */