os/os2: recursive directory walker, expose errors in read_directory, file clone

Adds a directory walker, a method of exposing and retrieving errors from
the existing read directory iterator, allows reusing of the existing
read directory iterator, and adds a file clone procedure

tests/core/os/os2/file.odin

@@ -0,0 +1,31 @@
+package tests_core_os_os2
+
+import os "core:os/os2"
+import    "core:testing"
+import    "core:path/filepath"
+
+@(test)
+test_clone :: proc(t: ^testing.T) {
+	f, err := os.open(filepath.join({#directory, "file.odin"}, context.temp_allocator))
+	testing.expect_value(t, err, nil)
+	testing.expect(t, f != nil)
+
+	clone: ^os.File
+	clone, err = os.clone(f)
+	testing.expect_value(t, err, nil)
+	testing.expect(t, clone != nil)
+
+	testing.expect_value(t, os.name(clone), os.name(f))
+	testing.expect(t, os.fd(clone) != os.fd(f))
+
+	os.close(f)
+
+	buf: [128]byte
+	n: int
+	n, err = os.read(clone, buf[:])
+	testing.expect_value(t, err, nil)
+	testing.expect(t, n > 13)
+	testing.expect_value(t, string(buf[:13]), "package tests")
+
+	os.close(clone)
+}