Ensure CefSettings.CachePath and RequestContextSettings.CachePath are absolute

[amaitland]

The cache path must be an absolute path. It was never intended to work with relative paths.

As per https://bitbucket.org/chromiumembedded/cef/issues/2916/not-persisting-in-local-stoage-when-using#comment-56993126 the CachePath must be absolute.

• throw Exception if paths are non absolute

Related issue #3074

[amaitland]

Another option would be to validate the path provided and throw an exception. This may be the slightly less user friendly option, it would avoid any potential issues where the Path.GetFullPath was to resolve incorrectly.

https://docs.microsoft.com/en-us/dotnet/api/system.io.path.ispathrooted?view=netframework-4.8

[amaitland]

Browsersubprocess must also be absolute now

https://bitbucket.org/chromiumembedded/cef/commits/dede95c5866fee73db7fb0e5f2077fb2135db6ac

[amaitland]

The exception in https://github.com/cefsharp/CefSharp/blob/master/CefSharp.Core/Cef.h#L204 should be updated to make it clear an absolute path is required also.

[amaitland]

Resolved in 98b7abe