improve ancestor_id

[lukasdreyer]

Closes #1905

Describe your changes here:
Improve the calculation of the ancestor id by avoiding computing all information in the ancestor

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.16%. Comparing base (c5e2676) to head (bb8e4e4).

Additional details and impacted files

@@                        Coverage Diff                         @@
##           enhancement-standalone_type_uint8    #1903   +/-   ##
==================================================================
  Coverage                              76.15%   76.16%           
==================================================================
  Files                                    103      103           
  Lines                                  19424    19430    +6     
==================================================================
+ Hits                                   14792    14798    +6     
  Misses                                  4632     4632           

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[holke]

Looks good to me.
Would love to have some comments to explain the computation.

Also suggested a minor change.

[holke]

Suggested change

	int child_id;
	if constexpr (T8_ELEMENT_NUM_EQUATIONS[TEclass]) {
	u_int8_t type = element_compute_type_at_level (el, level);
	child_id = t8_element_type_cubeid_to_Iloc<TEclass>[type][cube_id];
	}
	else {
	child_id = cube_id;
	}
	return child_id;
	if constexpr (T8_ELEMENT_NUM_EQUATIONS[TEclass]) {
	u_int8_t type = element_compute_type_at_level (el, level);
	return t8_element_type_cubeid_to_Iloc<TEclass>[type][cube_id];
	}
	else {
	return cube_id;
	}

[holke]

Could you please add some comments to explain the formula?