Add Bresenham Line Algorithm to GridMap Drawing

[mchlopecki]

Implements #11995 for painting and erasing in GridMap.

Before:

This PR:

[fire]

Cool. I want to say this is a great enhancement. Will see if I can expedite review somehow.

[Calinou]

This PR fails to compile when rebased on top of master:

Compiling modules/gridmap/editor/grid_map_editor_plugin.cpp ...
Compiling editor/scene/3d/gizmos/.scu/scu_editor_scene_3d_gizmos.gen.cpp ...
modules/gridmap/editor/grid_map_editor_plugin.cpp: In member function 'bool GridMapEditor::do_input_action(Camera3D*, const Point2&, bool)':
modules/gridmap/editor/grid_map_editor_plugin.cpp:442:54: error: 'class LocalVector<GridMapEditor::SetItem>' has no member named 'back'
  442 |                         Vector3i last_si = set_items.back()->get().position;
      |                                                      ^~~~
Generating core/version_hash.gen.cpp ...
scons: *** [bin/obj/modules/gridmap/editor/grid_map_editor_plugin.linuxbsd.editor.x86_64.o] Error 1
scons: building terminated because of errors.

This is due to set_items now being a LocalVector since https://docs.godotengine.org/en/stable/contributing/workflow/pr_workflow.html#the-interactive-rebase was merged. LocalVector does not have a back() method (see #99955), so you need to replace it with something else.

See this page for instructions on rebasing the PR.

[Calinou]

Tested locally on all edit axes, it works as expected. Code looks good to me.

Top is drawn without this PR, bottom is drawn with this PR (at a similar mouse speed for each). The editor is capped at 30 FPS for this demonstration, which will make the issue more noticeable (the lower the FPS, the more likely your cursor will be missing tiles).

Note that visible polygon edges will occur at low FPS, given your mouse cursor position is only sampled once per rendered frame. A more extensive solution could disable input accumulation when drawing in the GridMap editor, then using all the input positions recorded in a single frame to draw the tiles at the mouse's real position, which should lead to smoother curves. That said, this is not essential for an initial implementation, as it already helps a lot, especially when drawing straight (or mostly straight) lines.

[mchlopecki]

I've implemented changes, rebased on master and tested for general functionally one more time. Unless there are any other notes/changes, it should be ready for merging once it passes CI/CD.

[Repiteo]

Could you rebase your PR? See our pull request guidelines for more information

[Chaosus]

@Repiteo I've rebased it ^^ seems to work fine

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉