MDEV-31554 Cursor protocol cuts off json boolean

[grooverdan]

In Item_func_json_array_append::fix_length_and_dec, Item_bool::max_char_length() was being used to
calculate the length that is required to fit a boolean.

Previously it was returning 1, which doesn't fit "false".

Change Item_bool to return strlen("false"), 5.

[gemini-code-assist]

Code Review

This pull request enables cursor protocol tests in func_json.test and increases the length parameter from 1 to 5 in one of the Item_bool constructors in sql/item.h to prevent truncation. The reviewer recommends updating the other Item_bool constructors to consistently use a length of 5 to avoid similar truncation issues when those constructors are used.

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[gemini-code-assist]

The other constructors of Item_bool still initialize Item_int with a length of 1. To prevent the same truncation issue when Item_bool is instantiated using these other constructors, all of them should be updated to use a length of 5 (to fit "false").

  Item_bool(THD *thd, const char *str_arg, longlong i):
    Item_int(thd, str_arg, i, 5) {}
  Item_bool(THD *thd, bool i) :Item_int(thd, (longlong) i, 5) { }
  Item_bool(const char *str_arg, longlong i):
    Item_int(str_arg, i, 5) {}