Repository: opencv
Issue: getCacheDirectoryForDownloads throws exception when encountering unicode paths
Labels: bug,platform: win32

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##### System information (version)
<!-- Example
- OpenCV => 4.2
- Operating System / Platform => Windows 64 Bit
- Compiler => Visual Studio 2017
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- OpenCV => 4.2
- Operating System / Platform => Windows 11
- Compiler => Visual Studio 2019

##### Detailed description

`getCacheDirectoryForDownloads` uses `GetTempPathA` on Windows.

It uses the environment variable `TMP`.

Default: `C:\Users\username\AppData\Local\Temp`

`getCacheDirectoryForDownloads` throws an exception when the `username` contains unicode characters.

E.g: `C:\Users\流星暴雨\AppData\Local\Temp`

##### Steps to reproduce

```py
# -*- coding: utf-8 -*-

import tempfile
import cv2

os.environ["TMP"] = tempfile.mkdtemp("测试")
print(cv2.utils.fs.getCacheDirectoryForDownloads())
```

```
PS F:\opencv_test> python .\1.py
Traceback (most recent call last):
  File "F:\opencv_test\1.py", line 10, in <module>
    print(cv2.utils.fs.getCacheDirectoryForDownloads())
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xc1 in position 9: invalid start byte
```

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