Fix some TileMap debug drawing truncating to ints

[kleonc]

Fixes part of #87138 (besides the incorrect generation of the navigation polygon (see #87138 (comment))).

• quadrant_pos was correctly calculated as Vector2 but it was converted to Vector2i when passing to _X_draw_cell_debug methods:
  

  godot/scene/2d/tile_map_layer.cpp

  Lines 126 to 136 in 26b1fd0

  	const Vector2 quadrant_pos = tile_map_node->map_to_local(debug_quadrant.quadrant_coords * TILE_MAP_DEBUG_QUADRANT_SIZE);
  	Transform2D xform(0, quadrant_pos);
  	rs->canvas_item_set_transform(ci, xform);
  	for (SelfList<CellData> *cell_data_list_element = debug_quadrant.cells.first(); cell_data_list_element; cell_data_list_element = cell_data_list_element->next()) {
  	CellData &cell_data = *cell_data_list_element->self();
  	if (cell_data.cell.source_id != TileSet::INVALID_SOURCE) {
  	_rendering_draw_cell_debug(ci, quadrant_pos, cell_data);
  	_physics_draw_cell_debug(ci, quadrant_pos, cell_data);
  	_navigation_draw_cell_debug(ci, quadrant_pos, cell_data);
  	_scenes_draw_cell_debug(ci, quadrant_pos, cell_data);

• Rect2i::get_center returning Vector2i instead of Vector2 strikes again. This time making the offset for the texture region center being calculated incorrectly.
  Still no idea why this method works like that. For me it's like if Vector2i::length would be returning int instead of float etc. 🙃 Maybe we could/should add something like Rect2i::get_centerf? 🤔 (assuming Rect2i::get_center can't be changed because of compat)

debug drawing	Before (v4.3.dev1.official [9d1cbab])	After (this PR)
Physics - rendering offsets fixed
Navigation - rendering offsets fixed - still incorrect polygon generated

Haven't tested this thoroughly so not sure if maybe something else got broken/revealed incorrect offset calculation or something like that.

[JekSun97]

I hope the Godot team will no longer rewrite the entire engine :D

[akien-mga]

Thanks!