Add built-in logging capabilities

[pwab]

Describe the project you are working on:
N/A (generic issue)

Describe the problem or limitation you are having in your project:
I do use logging a lot to track things in the game and investigate bugs. But I don't believe that I do that in an efficient way (or that there's such way at all for GDScript) while simply using the print function.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
See original issue: godotengine/godot#27958

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:
An existing logger can be found here: https://github.com/hedin-hiervard/godot-logger
(Or take some ideas from the Unity logger maybe)

If this enhancement will not be used often, can it be worked around with a few lines of script?:
I'm pretty sure it would be used quite often.

Is there a reason why this should be core and not an add-on in the asset library?:
Print-debugging is used all over the place. At least a simple logger would help to solve most of the problems mentioned in the original issue (formatting, categories, destination).

Original issue: godotengine/godot#27958

[Calinou]

Closing in favor of #5954, which is more detailed.