[feat] nvim: add nvim-silicon plugin

Also reorganize out of tree plugins in preparation for
`vim-plugin-updater` integration.

nvim/extraPlugins/default.nix

@@ -0,0 +1,4 @@
+{pkgs}: {
+  vim-jjdescription = pkgs.callPackage ./vim-jjdescription.nix {};
+  nvim-silicon = pkgs.callPackage ./nvim-silicon.nix {};
+}

nvim/extraPlugins/nvim-silicon.nix

@@ -0,0 +1,15 @@
+{
+  vimUtils,
+  fetchFromGitHub,
+  silicon,
+}:
+vimUtils.buildVimPlugin {
+  name = "nvim-silicon";
+  dependencies = [silicon];
+  src = fetchFromGitHub {
+    owner = "michaelrommel";
+    repo = "nvim-silicon";
+    rev = "v1.0.0";
+    hash = "sha256-cZOzgzLUNC9qOS2m/rc6YJfpNGdRTSCAdEPQDy+wT6I=";
+  };
+}

nvim/extraPlugins/vim-jjdescription.nix

@@ -0,0 +1,13 @@
+{
+  vimUtils,
+  fetchFromGitHub,
+}:
+vimUtils.buildVimPlugin {
+  name = "jjdescription";
+  src = fetchFromGitHub {
+    owner = "avm99963";
+    repo = "vim-jjdescription";
+    rev = "c9bf9f849ead3961ae38ab33f68306996e64c6e8";
+    hash = "sha256-qnZFuXbzpm2GN/+CfksFfW2O+qTosUZcUagqCTzmtWo=";
+  };
+}