plugins: Introduce generated, static core plugin registry (#54118)

* Refactor towards template/codegen framework

* Add templates for plugin gen

* Add Go codegen for plugins; overhaul framework, too

* Add new codegen output; assorted framework fixes

* Regenerate after merge

* Remove accidental commit file, update templates

* Export the pfs.Tree loader from plugin types

* Print details from cuetsy errors

* Generate loaders for all plugins and list in registry

* Use pfs_gen.go over lineage_gen.go

* Un-un-ignore main file

* Introduce simple List static registry for plugins

* Last tweaks to codegen

* remove unused tvars

* Ensure loop-local instances for both vars

* Generate pfs parsing in-place in registry

* Stop generating pfs_gen.go

* Move Tree into pfs, rename subdir

* Change package name to match dir

* Ignore gocyclo on HTTPServer.getNavTree

packages/grafana-schema/src/schema/dashboard/dashboard_experimental.gen.ts

@@ -1,8 +1,10 @@
 // This file is autogenerated. DO NOT EDIT.
 //
-// Run "make gen-cue" from repository root to regenerate.
+// Generated by pkg/framework/coremodel/gen.go
 //
-// Derived from the Thema lineage at pkg/coremodel/dashboard
+// Derived from the Thema lineage declared in pkg/coremodel/dashboard/coremodel.cue
+//
+// Run `make gen-cue` from repository root to regenerate.
 
 
 // This model is a WIP and not yet canonical. Consequently, its members are