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/applications/editors/jetbrains/idea-plugins.nix

@@ -1,15 +1,29 @@
-{ callPackage }:
+{ lib, stdenv, fetchzip }:
+
+self:
+
 let
-  mkPlugin = callPackage ./build-plugin.nix {
+
+  ideaBuild = import ../../../build-support/jetbrains/plugin.nix {
+    inherit lib stdenv fetchzip;
     jetbrainsPlatforms = [ "idea-community" "idea-ultimate" ];
   };
-in
-{
-  spring-assistant = mkPlugin {
-    pname = "intellij-spring-assistant";
-    version = "0.12.0";
-    pluginId = 10229;
-    versionId = 44968;
-    sha256 = "13cglywzhb4j0qj0bs2jwaz2k8pxrxalv35wgkmgkxr635bxmwsj";
-  };
-}
+
+  generateIdea = lib.makeOverridable ({
+    idea ? ./manual-idea-packages.nix
+  }: let
+
+    imported = import idea {
+      inherit (self) callPackage;
+    };
+
+    super = imported;
+
+    overrides = { };
+
+    ideaPlugins = super // overrides;
+
+  in ideaPlugins // { inherit ideaBuild; });
+
+in generateIdea { }
+