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/build-support/jetbrains/plugin.nix

@@ -0,0 +1,33 @@
+{ lib
+, stdenv
+, fetchzip
+, jetbrainsPlatforms
+}:
+
+{ pluginId
+, pname
+, version
+, versionId
+, sha256
+, filename ? "${pname}-${version}.zip"
+}:
+
+stdenv.mkDerivation {
+  inherit pname version;
+
+  src = fetchzip {
+    inherit sha256;
+    url = "https://plugins.jetbrains.com/files/${toString pluginId}/${toString versionId}/${filename}";
+  };
+
+  passthru = { inherit jetbrainsPlatforms; };
+
+  installPhase = ''
+    mkdir $out
+    cp -r * $out/
+  '';
+
+  meta = {
+    homepage = "https://plugins.jetbrains.com/plugin/${pluginId}-${lib.toLower pname}";
+  };
+}