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/modules/misc/version.nix

@@ -23,14 +23,14 @@ in
     nixos.release = mkOption {
       readOnly = true;
       type = types.str;
-      default = trivial.version;
+      default = trivial.release;
       description = "The NixOS release (e.g. <literal>16.03</literal>).";
     };
 
     nixos.versionSuffix = mkOption {
       internal = true;
       type = types.str;
-      default = trivial.suffix;
+      default = trivial.versionSuffix;
       description = "The NixOS version suffix (e.g. <literal>1160.f2d4ee1</literal>).";
     };