Improve ecma_string_t descriptor (#3016)

This patch introduces several changes conntect to ecma-strings:
 - Extend the size of the reference counter to 28 bytes from 13
 - Extend the size of the string hash to 32 bytes from 16 to use the extact FNV-1a hash
 - Introduce ECMA_STATIC_STRING_FLAG to reduce the number of string ref/derefs for static strings.
 - Introduce ECMA_STRING_CONTAINER_ASCII_STRING to store run-time allocated ASCII strings more efficiently
 - Remove ECMA_STRING_CONTAINER_LIT_NUMBER to half the storage size of the parsing time allocated floating point numbers
 - Rework the global number storage, to store only the floating point numbers
 - Optimize the lookup in the global number/string/symbol tables via reduce the number of NULL checks during decompressing the next element pointers
 - Reduce the code duplication in ecma_concat_ecma_strings and ecma_append_chars_to_string
 - Improve ecma_string_get_char with optional arguments to make it more reusable.

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

jerry-core/ecma/base/ecma-alloc.h

@@ -73,6 +73,18 @@ ecma_string_t *ecma_alloc_string (void);
  */
 void ecma_dealloc_string (ecma_string_t *string_p);
 
+/**
+ * Allocate memory for extended ecma-string descriptor
+ *
+ * @return pointer to allocated memory
+ */
+ecma_extended_string_t *ecma_alloc_extended_string (void);
+
+/**
+ * Dealloc memory from extended ecma-string descriptor
+ */
+void ecma_dealloc_extended_string (ecma_extended_string_t *string_p);
+
 /**
  * Allocate memory for string with character data
  *