Install an empty library (compat with dune3)

Dune 2 assumes that there's a "uchar" library installed by the compiler
but that is not true so it was removed in ocaml/dune#5260.

This means that a sourceless uchar package does not work: some sources
are necessary for `(libraries ... uchar)` to work.

This 0.0.2+dune3 version installs an empty library instead.

dune

@@ -0,0 +1,4 @@
+(library
+ (public_name uchar)
+ (wrapped false)
+ (modules))

dune-project

@@ -0,0 +1,3 @@
+(lang dune 1.1)
+(name uchar)
+(version 0.0.2+dune2)

opam → uchar.opam

@@ -7,8 +7,22 @@ dev-repo: "https://github.com/ocaml/uchar.git"
 bug-reports: "https://github.com/ocaml/uchar/issues"
 tags: [ "text" "character" "unicode" "compatibility" "org:ocaml.org" ]
 license: "typeof OCaml system"
-depends: [ "dune" "ocaml" {>= "4.03"} ]
+depends: [ "dune" {>= "1.1"} "ocaml" {>= "4.03"} ]
 synopsis: "Dummy but non virtual package to satisfy both opam-monorepo and opam"
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+]
 url {
   src: "git+https://github.com/dune-universe/uchar.git#dune-universe-v0.0.2"
 }