Use wchar_t API for windows file operation in standardpath

[wengxt]

Summary

It is well known about the encoding issue on windows. So prefer to use _w variant instead of POSIX ones on windows.

[wengxt]

Using std::filesystem::path instead of std::string will be part of this project, so we can get the native path char type for free.

[wengxt]

current plan is to create a new class for standard path at the same time, simplify the existing api and mark the o ld one as deprecated.

The pattern we really need are:

1. open a fixed file name (reloadConfig)
2. load all file with a pattern (e.g. all dict, all .conf). prefer to load one by one instead of open all at the same time. There was a bug that hit the os file descriptor limit.
3. timestamp we still need.
4. icon theme need the open all