add typesafe std/paths, std/files, std/dirs, std/symlinks (#20582)

* split std/os; add typesafe std/paths
* add more files, dirs, paths
* add documentation
* add testcase
* remove tryRemoveFile
* clean up
* Delete test.nim
* apply changes
* add `add` and fixes

tests/stdlib/tfilesanddirs.nim

@@ -0,0 +1,23 @@
+import std/[paths, files, dirs]
+
+from stdtest/specialpaths import buildDir
+import std/[syncio, assertions]
+
+block fileOperations:
+  let files = @[Path"these.txt", Path"are.x", Path"testing.r", Path"files.q"]
+  let dirs = @[Path"some", Path"created", Path"test", Path"dirs"]
+
+  let dname = Path"__really_obscure_dir_name"
+
+  createDir(dname.Path)
+  doAssert dirExists(Path(dname))
+ 
+  # Test creating files and dirs
+  for dir in dirs:
+    createDir(Path(dname/dir))
+    doAssert dirExists(Path(dname/dir))
+
+  for file in files:
+    let fh = open(string(dname/file), fmReadWrite) # createFile
+    fh.close()
+    doAssert fileExists(Path(dname/file))