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

pkg/codegen/tmpl/plugin_lineage_binding.tmpl

@@ -0,0 +1,12 @@
+// The current version of the coremodel schema, as declared in coremodel.cue.
+// This version determines what schema version is returned from [Coremodel.CurrentSchema],
+// and which schema version is used for code generation within the grafana/grafana repository.
+//
+// The code generator ensures that this is always the latest Thema schema version.
+var currentVersion{{ .SlotName }} = thema.SV({{ .LatestSeqv }}, {{ .LatestSchv }})
+
+// {{ .SlotName }}Lineage returns the Thema lineage for the {{ .PluginID }} {{ .PluginType }} plugin's
+// {{ .SlotName }} ["github.com/grafana/grafana/pkg/framework/coremodel".Slot] implementation.
+func {{ .SlotName }}Lineage(lib thema.Library, opts ...thema.BindOption) (thema.Lineage, error) {
+	return cuectx.LoadGrafanaInstancesWithThema(filepath.Join("public", "app", "{{ .Name }}"), cueFS, lib, opts...)
+}