Rename Camera2D's *_screen_center and *_position to get_screen_center_position and get_target_position

[Mickeon]

As brought up in: #54161 (comment), #54161 (comment).

I am fuming, how did I forget to write this sooner, dang it! I was the one complaining about it!

These Camera2D properties have very confusing and redundant names. Most egregiously, last time I edited the documentation, I had to carefully tip-toe around get_camera_position() to make sure it wasn't being confused with Node2D.position. This PR attempts to address that.

get_camera_screen_center -> get_screen_center_position
get_camera_position -> get_target_position

Also improves the documentation of these two.

Previously this PR was get_camera_screen_center -> get_screen_center
Note: Unlike other PRs similarly to this, I left their internal names untouched. See #63773.

[KoBeWi]

I was thinking if get_camera_position() is even needed. It does return some variable, but it's not very useful. It's a weird mix between global_position() and get_camera_screen_center().

[Mickeon]

It definitely is. I've used this method for fine-tuning, displaying the target position during debugging to better understand the internal behaviour, and in particular, I've required it to restore the camera exactly as it was after saving and reloading from a PackedScene. I really struggled to find it, however, because of the poor naming.

Definitely shouldn't be exposed as a full property, but it's really nice to have and see as is.

[akien-mga]

CC @madmiraal @lawnjelly

[Ansraer]

During the meeting, we agreed to remove the camera suffix, but couldn't agree on the exact naming.
get_screen_center_global_position and get_target_global_position were proposed, but we couldn't agree on whether that was too verbose.

[madmiraal]

I think adding global is unnecessary. The camera only works in global coordinates. There are no equivalent methods returning local coordinates.

[Mickeon]

So it should then be get_screen_center_position? Okiedokie

[akien-mga]

Approved in PR review meeting.

[akien-mga]

Thanks!