codegen: Introduce TS codegen veneer (#54816)

* Split all named types out into defs, etc.

* Use latest cuetsy, refactor generators accordingly

* Return AST type from plugin TS generator

* Near-complete checkin of TS veneer code generator

* First full completed pass

* Improve the attribute name

* Defer use of the dashboard veneer type to follow-up

* Remove dummy index, prettier on veneer

* Fix merge errors in gen.go

* Add match field to SpecialValueMap

* Fix backend lint errors

pkg/codegen/tmpl/cuetsy_multi.tmpl

@@ -1,7 +1,2 @@
 {{ template "autogen_header.tmpl" .Header -}}
-{{range .Imports}}
-import * as {{.Ident}} from '{{.Pkg}}';{{end}}
-{{range .Sections}}{{if ne .ModelName "" }}
-export const {{.ModelName}}ModelVersion = Object.freeze([{{index .V 0}}, {{index .V 1}}]);
-{{end}}
-{{.Body}}{{end}}
+{{ .Body }}