Improve error reporting of ProjectSettings::setup()

[akien-mga]

And use it to better report errors in the console and project manager
when a project.godot file is corrupted.

Fixes #14963.

---

Apart from fixing the referenced corner case issue, this new Error output is not used much yet, but I think that the code is cleaner and it will be useful to debug ProjectSettings::setup() to have it report the right error code.

I tried to retrieve the error code in main.cpp, but I got conflicts with the goto stuff... not sure how to go around it. Namely this diff:

diff --git a/main/main.cpp b/main/main.cpp
index a4ef35754..e48d4fd78 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -751,7 +751,8 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 
 #endif
 
-       if (globals->setup(game_path, main_pack, upwards) != OK) {
+       Error err = globals->setup(game_path, main_pack, upwards);
+       if (err != OK) {
 
 #ifdef TOOLS_ENABLED
                editor = false;

Triggers this error:

main/main.cpp: In static member function 'static Error Main::setup(const char*, int, char**, bool)':
main/main.cpp:967:1: error: jump to label 'error' [-fpermissive]
 error:
 ^
main/main.cpp:724:9: note:   from here
    goto error;
         ^
main/main.cpp:754:8: note:   crosses initialization of 'Error err'
  Error err = globals->setup(game_path, main_pack, upwards);
        ^
main/main.cpp:967:1: error: jump to label 'error' [-fpermissive]
 error:
 ^
main/main.cpp:373:9: note:   from here
    goto error;
         ^
main/main.cpp:754:8: note:   crosses initialization of 'Error err'
  Error err = globals->setup(game_path, main_pack, upwards);
        ^

(and I checked, it's not a naming issue, using int as type or mycustomerr as variable name triggers the same issue)

[akien-mga]

Seems like this broke loading .pck files as noticed by @AndreaCatania. I'll look into fixing it tonight if nobody beats me to it.

[akien-mga]

Fixed with 57d562b. Damn unreliable error reporting :p