Fix printerr

[fenix-hub]

On some exports without debug mode enabled, printerr function freezes the build.
printerr and print_debug have been replaced with a custom _printerr function implemented by Firebase, so that any Firebase module (and also users) can call that function.
Firebase._printerr(error : String) adds an header identifying that the source of the error is Firebase.

Godot Engine v3.3.rc9.official - https://godotengine.org
OpenGL ES 3.0 Renderer: Intel(R) HD Graphics 520
OpenGL ES Batching: ON

[Firebase Error] >> Configuration key 'measurementId' not found!
[Firebase Error] >> Configuration key 'clientId' not found!
[Firebase Error] >> Configuration key 'clientSecret' not found!
[Firebase Error] >> Configuration key 'domainUriPrefix' not found!
[Firebase Error] >> Configuration key 'cacheLocation' not found!

[Firebase Error] >> Unauthenticated request issued...
[Firebase Error] >> Client authenticated as Anonymous User.
[Firebase Error] >> Document already exists: projects/roundtable-5c241/databases/(default)/documents/allusers4/timestamp