Item_decimal_typecast::print properly implemented


mysql-test/r/view.result:
  Bug #27921 View ignores precision for CAST()
  test result
mysql-test/t/view.test:
  Bug #27921 View ignores precision for CAST()
  test case
sql/field.cc:
  zero decimals handling unified
sql/item_create.cc:
  Bug #27921 View ignores precision for CAST()
  create_func_cast parameters changed, zero precision handling unified
sql/item_create.h:
  Bug #27921 View ignores precision for CAST()
  create_func_cast parameters changed
sql/item_func.cc:
  Bug #27921 View ignores precision for CAST() 
  Item_decimal_typecast::print properly implemented
sql/item_func.h:
  Bug #27921 View ignores precision for CAST()
  max_length counting fixed
sql/my_decimal.h:
  Bug #27921 View ignores precision for CAST()
  my_decimal_trim() implemented to unify zero precision handling
sql/sql_yacc.yy:
  Bug #27921 View ignores precision for CAST()
  create_func_cast calls simplified