treewide: rename version attributes

As suggested in https://github.com/NixOS/nixpkgs/pull/39416#discussion_r183845745
the versioning attributes in `lib` should be consistent to
`nixos/version` which implicates the following changes:

* `lib.trivial.version` -> `lib.trivial.release`
* `lib.trivial.suffix` -> `lib.trivial.versionSuffix`
* `lib.nixpkgsVersion` -> `lib.version`

As `lib.nixpkgsVersion` is referenced several times in `NixOS/nixpkgs`,
`NixOS/nix` and probably several user's setups. As the rename will cause
a notable impact it's better to keep `lib.nixpkgsVersion` as alias with
a warning yielded by `builtins.trace`.

nixos/maintainers/scripts/ec2/create-amis.sh

@@ -6,7 +6,7 @@
 set -e
 set -o pipefail
 
-version=$(nix-instantiate --eval --strict '<nixpkgs>' -A lib.nixpkgsVersion | sed s/'"'//g)
+version=$(nix-instantiate --eval --strict '<nixpkgs>' -A lib.version | sed s/'"'//g)
 major=${version:0:5}
 echo "NixOS version is $version ($major)"