C#: Fix line in OpenInExternalEditor

[raulsntos]

• Fixes C# Error message point to one line above in Visual Studio Code #41816.
• ⚠️ Only tested this with VSCode, I hope I didn't break other IDEs ⚠️
• Note for 3.x cherrypick: Requires also cherry-picking C#: Fix line position when opening file in VSCode #73584.

[RedworkDE]

This also works in VS, but the built-in editor now points to the line above.

[raulsntos]

I looked into this and reached the conclusion that EditorInterface::edit takes a 1-based line number, and every other API (ScriptEditor, CodeTextEditor and TextEditor) takes a 0-based line number.

The ScriptEditor::edit method was subtracting 1 from the line number which seems to be wrong, since every other API in ScriptEditor seems to be 0-based. This was causing the double subtract that made this PR break with the built-in editor.

The double subtract should also be happening with GDScript errors, but in there there is a call to goto_line_centered after the call to edit which essentially resets the line to right one thus hiding the bug.

As a consequence of these changes this is likely no longer cherry-pickable for 3.x and I have removed the label. If this change is desired for 3.x, a backport PR can be made.

[RedworkDE]

Didn't notice any more issues

[akien-mga]

Thanks!

[YuriSizov]

Cherry-picked for 4.1.3.