[PATCH v3 0/1] MR2081: Support relocatable fontconfig cache

[catsout (＠catsout)]

For flatpak:  
```
bind mount:
/run/host/fonts      <- /usr/share/fonts
/run/host/user-fonts <- ~/.local/share/fonts

/run/host/fonts-cache      <- /usr/lib/fontconfig/cache
/run/host/user-fonts-cache <- ~/.cache/fontconfig
```

For fontconfig:   
https://bugs.freedesktop.org/show_bug.cgi?id=101889  
https://github.com/flatpak/flatpak/issues/589  
It supports relocatable cache.  
```
FcConfigGetFontDirs( config )  -> /run/host/user-fonts/test,...
FcDirCacheRead( /run/host/user-fonts/test, ... ) -> FcCacheCopySet -> pattern
FcPatternGetString( pattern, FC_FILE, 0, &filename ) -> ~/.local/share/fonts/test/test.ttf
```

For wine:  
``` 
FcPatternGetString -> unix_name -> add_unix_face( unix_name, ... )  
```
The valid file path for flatpak is `/run/host/user-fonts/test/test.ttf`.  
`~/.local/share/fonts/test/test.ttf` does not exist in flatpak sandbox.

Add a check for this, and switch to right path.

Test:  
```
flatpak install org.winehq.Wine
LANG=zh_CN.UTF-8 flatpak run org.winehq.Wine winecfg
```
![image](/uploads/6679b2771e3400b02903faa308a1d1c5/image.png)

--
  v3: Support relocatable fontconfig cache

https://gitlab.winehq.org/wine/wine/-/merge_requests/2081