Add public_name's to all dune sub libraries

These will all live under the jbuilder package

src/configurator/jbuild

@@ -1,5 +1,6 @@
 (library
  ((name configurator)
+  (public_name jbuilder.configurator)
   (libraries (stdune ocaml_config))
   (flags (:standard -safe-string (:include flags/flags.sexp)))
   (preprocess no_preprocessing)))

src/ocaml-config/jbuild

@@ -2,5 +2,6 @@
 
 (library
  ((name      ocaml_config)
+  (public_name jbuilder.ocaml_config)
   (libraries (stdune usexp))
   (synopsis  "Interpret the output of 'ocamlc -config'")))

src/stdune/caml/jbuild

@@ -1,3 +1,4 @@
 (library
  ((name caml)
+  (public_name jbuilder.caml)
   (synopsis "Wrapped version of the OCaml stdlib")))

src/stdune/jbuild

@@ -1,4 +1,5 @@
 (library
  ((name stdune)
+  (public_name jbuilder.stdune)
   (synopsis "Standard library of Dune")
   (libraries (caml unix))))

src/usexp/jbuild

@@ -1,6 +1,8 @@
 (jbuild_version 1)
 
-(library ((name usexp)))
+(library
+ ((name usexp)
+  (public_name jbuilder.usexp)))
 
 (rule
  (with-stdout-to table.ml.gen (run gen/gen_parser_automaton.exe)))