plugins: Move plugin definitions to avoid monkey patching

Also document the plugin data structures.

src/static/js/pluginfw/plugin_defs.js

@@ -0,0 +1,24 @@
+// This module contains processed plugin definitions. The data structures in this file are set by
+// plugins.js (server) or client_plugins.js (client).
+
+// Maps a hook name to a list of hook objects. Each hook object has the following properties:
+//   * hook_name: Name of the hook.
+//   * hook_fn: Plugin-supplied hook function.
+//   * hook_fn_name: Name of the hook function, with the form <filename>:<functionName>.
+//   * part: The ep.json part object that declared the hook. See exports.plugins.
+exports.hooks = {};
+
+// Whether the plugins have been loaded.
+exports.loaded = false;
+
+// Topologically sorted list of parts from exports.plugins.
+exports.parts = [];
+
+// Maps the name of a plugin to the plugin's definition provided in ep.json. The ep.json object is
+// augmented with additional metadata:
+//   * parts: Each part from the ep.json object is augmented with the following properties:
+//       - plugin: The name of the plugin.
+//       - full_name: Equal to <plugin>/<name>.
+//   * package (server-side only): Object containing details about the plugin package (version,
+//     path).
+exports.plugins = {};