Improve Timer error messages

[Calinou]

• Mention the node path (or node name if not in tree).
• Mention the provided invalid wait time.

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• This addresses [TRACKER] Error macros with cryptic messages due to not having proper custom messages defined #42719 (comment).

Testing project: test_timer_error_messages.zip

Preview

Before

ERROR: Timer was not added to the SceneTree. Either add it or set autostart to true.
   at: start (scene/main/timer.cpp:109)

ERROR: Time should be greater than zero.
   at: set_wait_time (scene/main/timer.cpp:83)

After

ERROR: Timer (out-of-tree): Timer was not added to the SceneTree. Either add it to the SceneTree using `add_child()`, or set the `autostart` property to `true`.
   at: start (./scene/main/timer.cpp:109)

ERROR: Timer2 (out-of-tree): The wait time should be greater than 0 seconds, but a wait time of -0.500000 was provided.
   at: set_wait_time (./scene/main/timer.cpp:83)

[Calinou]

Note that this would benefit from Node.get_debug_path(), which I added in #95579. This way, we can reduce code repetition significantly, as a lot of messages will eventually benefit from printing out node paths (and falling back to the node name if out-of-tree).