shared/runtime/sys_stdio_mphal: Fix printed type for stdio streams.

The printed type for stdio streams indicates "FileIO", which is a binary IO
stream.  Stdio is not binary by design, and its printed type should
indicate a text stream.  "TextIOWrapper" suits that purpose, and is used
by VfsPosix files.

Signed-off-by: timdechant <timdechant.git@gmail.com>

tests/basics/sys_stdio_buffer.py

@@ -0,0 +1,21 @@
+# Test sys.std*.buffer objects.
+
+import sys
+
+try:
+    sys.stdout.buffer
+    sys.stdin.buffer
+    sys.stderr.buffer
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
+# CPython is more verbose; no need to match exactly
+
+print('FileIO' in str(sys.stdout.buffer))
+print('FileIO' in str(sys.stderr.buffer))
+print('FileIO' in str(sys.stdin.buffer))
+
+print('FileIO' in str(type(sys.stdout.buffer)))
+print('FileIO' in str(type(sys.stderr.buffer)))
+print('FileIO' in str(type(sys.stdin.buffer)))