We will now try
1. cacheDir (or, commonly set in environment as `HUGO_CACHEDIR`)
2. if on Netlify we use `/opt/build/cache/hugo_cache/`
3. os.UserCacheDir
4. A temp dir
Storing the cache, especially the module cache, in a temporary idea has had lots of hard to debug issues, especially on MacOS,
which this commit tries to fix.
This should also make it easier to locate the Hugo cache:
>UserCacheDir returns the default root directory to use for user-specific cached data. Users should create their own
application-specific subdirectory within this one and use that.
>
>On Unix systems, it returns $XDG_CACHE_HOME as specified by
https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if non-empty, else $HOME/.cache. On Darwin, it
returns $HOME/Library/Caches. On Windows, it returns %LocalAppData%. On Plan 9, it returns $home/lib/cache.
>
>If the location cannot be determined (for example, $HOME is not defined), then it will return an error.
Fixes#11286Fixes#11291
