Cryptic error message when addMenuItem() is passed bad args

[peterflynn]

1. Install the BracketLESS extension
2. Quit & relaunch Brackets

Result:
Console contains error "addMenuItem() -- error: 3 when adding command: bracketless.enabled" indicating an error code returned from brackets.app.addMenuItem().

Expected:
BracketLESS is doing something wrong here: passing a nonexistent command id as the relativeID arg. However, before the native menu migration we gave much more informative error strings. In this case it would have been "_getRelativeMenuItem(): MenuItem with Command id menu-view-sidebar not found in Menu view-menu". The message we actually show is uninformative and almost looks like brackets-shell bug rather then a problem with the extension's code.

[njx]

Reviewed. Low priority to @gruehle. Glenn, do you think this could be a starter bug? Could it be fixed purely on the JS side by mapping the error codes to strings, or is there more info we'd need to get from the native side in order to provide good errors?

[redmunds]

FBNC back to @peterflynn . @TomMalbran fixed this on the JS side.