jetbrains: rework following the Emacs builder

This commit moves a lot of the heavy lifting out of callPackage and back
into regular import, following conventions from upstream Nixpkgs. It
allows for a clearer and less magic definition of new packages,
particularly by downstream, as well, by exposing the *Build package
callers in the attribute set.

pkgs/top-level/jetbrains-plugins.nix

@@ -0,0 +1,33 @@
+{ lib
+, newScope
+, stdenv
+, fetchzip
+
+, variant
+}:
+
+let
+
+  mkJetbrainsPlugins = import ../applications/editors/jetbrains/common-plugins.nix {
+    inherit lib stdenv fetchzip;
+  };
+
+  mkIdeaPlugins = import ../applications/editors/jetbrains/idea-plugins.nix {
+    inherit lib stdenv fetchzip;
+  };
+
+  jetbrainsWithPlugins = import ../applications/editors/jetbrains/wrapper.nix {
+    inherit lib;
+  };
+
+in lib.makeScope newScope (self: lib.makeOverridable ({
+  jetbrainsPlugins ? mkJetbrainsPlugins self
+  , ideaPlugins ? mkIdeaPlugins self
+}: ({ }
+  // jetbrainsPlugins // { inherit jetbrainsPlugins; }
+  // ideaPlugins // { inherit ideaPlugins; }
+  // {
+    inherit variant;
+    jetbrainsWithPlugins = jetbrainsWithPlugins self variant;
+  })
+) { })