Add static types in 2D Navigation A Star demo

[MatrixFrog]

I was just looking at this demo and realized that jumping to definitions of things would work a little better if the types were filled in, so I went ahead and did it.

Part of #868

[dalexeev]

Please add void type hints for all functions in character.gd and 2 functions in pathfind_astar.gd, float for unused parameter _delta. Also please add type hints or at least type inference for local variables arrived_to_next_point in _process(), last_point and current_point in _draw().

[dalexeev]

The changes look good to me, but I'm not sure we've reached consensus on #868. Personally, I support static typing in demo projects and find it improves readability. However, I recognize the concerns and think we should first define the rules for using static typing in demo projects.

There are also questions about type inference if the initializer does not contain the type name and whether it is necessary to specify the type for for loop variables (a new feature in 4.2).

[aaronfranke]

When the type is not written on the same line, it should be explicitly specified. https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_styleguide.html#inferred-types

Also this PR has conflicts and needs to be rebased.

[MatrixFrog]

Thanks. I should have time to test this out in a couple days.

[MatrixFrog]

ok just tested it out, this seems to be working well and should be ready to merge! thanks!

[aaronfranke]

I didn't test this but it looks correct.

[Calinou]

Tested locally, it works as expected.

Thanks!