[cleanup, utils] Split into submodules (#7090)

Closes https://github.com/yt-dlp/yt-dlp/pull/2173

Authored by: pukkandan, coletdjnz
Co-authored-by: pukkandan <pukkandan.ytdlp@gmail.com>

yt_dlp/utils/_deprecated.py

@@ -0,0 +1,30 @@
+"""Deprecated - New code should avoid these"""
+
+from ._utils import preferredencoding
+
+
+def encodeFilename(s, for_subprocess=False):
+    assert isinstance(s, str)
+    return s
+
+
+def decodeFilename(b, for_subprocess=False):
+    return b
+
+
+def decodeArgument(b):
+    return b
+
+
+def decodeOption(optval):
+    if optval is None:
+        return optval
+    if isinstance(optval, bytes):
+        optval = optval.decode(preferredencoding())
+
+    assert isinstance(optval, str)
+    return optval
+
+
+def error_to_compat_str(err):
+    return str(err)