fix setCommand so it behaves like regular nim invocation (#18555)

compiler/scriptconfig.nim

@@ -151,18 +151,9 @@ proc setupVM*(module: PSym; cache: IdentCache; scriptName: string;
     setResult(a, strutils.cmpIgnoreCase(a.getString 0, a.getString 1))
   cbconf setCommand:
     conf.setCommandEarly(a.getString 0)
-    # xxx move remaining logic to commands.nim or other
     let arg = a.getString 1
     incl(conf.globalOptions, optWasNimscript)
-    if arg.len > 0:
-      conf.projectName = arg
-      let path =
-        if conf.projectName.isAbsolute: AbsoluteFile(conf.projectName)
-        else: conf.projectPath / RelativeFile(conf.projectName)
-      try:
-        conf.projectFull = canonicalizePath(conf, path)
-      except OSError:
-        conf.projectFull = path
+    if arg.len > 0: setFromProjectName(conf, arg)
   cbconf getCommand:
     setResult(a, conf.command)
   cbconf switch: