clang: Make sure completion priority is properly fine grained
We are squeezing a 0-80 priority range into 0-10 one, all integers. This makes it easy for us to lose information rather soon.
Since we are only setting the MatchQuality for those Clang claims to be between 0-20 (i.e. under CCP_SuperCompletion), we can narrow our conversion to 0-20 too.
This allows us to properly sort some items that clang was properly sorting but we were unable to express correctly.
Edited by Aleix Pol Gonzalez