Add workingDir parameter to execProcess and test (#9549)

* Add workingDir parameter to execProcess
* Fix tests/stdlib/tosproc.nim compile error
* Suppress output from tosproc.nim

tests/stdlib/osproctest.nim

@@ -0,0 +1,8 @@
+# This is test program for the osproc module.
+
+import os
+
+echo getCurrentDir()
+
+for i in 1..paramCount():
+  echo paramStr(i)

tests/stdlib/tosproc.nim

@@ -0,0 +1,24 @@
+discard """
+  file: "tospaths.nim"
+  output: ""
+"""
+# test the osproc module
+
+import os, osproc
+
+block execProcessTest:
+  let dir = parentDir(currentSourcePath())
+  let (outp, err) = execCmdEx("nim c " & quoteShell(dir / "osproctest.nim"))
+  doAssert err == 0
+  let exePath = dir / addFileExt("osproctest", ExeExt)
+  let outStr1 = execProcess(exePath, workingDir=dir, args=["foo", "b A r"], options={})
+  doAssert outStr1 == dir & "\nfoo\nb A r\n"
+
+  const testDir = "t e st"
+  createDir(testDir)
+  doAssert dirExists(testDir)
+  let outStr2 = execProcess(exePath, workingDir=testDir, args=["x yz"], options={})
+  doAssert outStr2 == absolutePath(testDir) & "\nx yz\n"
+
+  removeDir(testDir)
+  removeFile(exePath)