Shader compilation failure -> show a detailed error message

[ChaoticByte]

For now Fragmented can only check if shader compilation failed by using a hacky workaround without a detailed error message.
Continuation of #16

[ChaoticByte]

Alternative way:

https://docs.godotengine.org/en/stable/classes/class_renderingdevice.html
https://docs.godotengine.org/en/stable/classes/class_rdshadersource.html

This most probably requires big code changes and low level shit I don't yet know about, but provides a cleaner, less hacky way to apply shaders to the image(s).
Wouldn't be Godot Shaders tho.

[ChaoticByte]

godotengine/godot-proposals#3000 (comment)

-> Created proposal godotengine/godot-proposals#11416 -> waiting