The file name should be hashed by md5 if it has multi-byte chars

[ryotsun]

If we download whole WordPress into Windows machine, file names will be broken if it has multi-byte chars.

Because Japanese version of Windows uses the SJIS for a filename.
I guess there are similar problems with another languages.

I asked to try test to some people and I saw this problem happen on Windows 10.

Related #44541, #44296

[miyauchi]

I created a list of tickets related to fix multibyte problems.

​https://docs.google.com/spreadsheets/d/13oGbc7AqEN6OUvmze-JDCKXDdruFqsxqSAdI7-b6Lho/edit#gid=0

[SergeyBiryukov]

Hi @ryotsun, welcome to WordPress Trac!

Thanks for the report, we're already tracking this issue in #15955 and #22363.