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

.gitignore

@@ -169,6 +169,8 @@ compilation-stats.json
 !pkg/services/featuremgmt/toggles_gen.go
 !pkg/coremodel/**/*_gen.go
 !pkg/framework/**/*_gen.go
+!pkg/plugins/pfs/**/*_gen.go
+!public/app/plugins/**/*_gen.go
 
 # Auto-generated internationalization files
 public/locales/_build/