Generate french_law artifacts through dune

The files where manually generated through Makefile rules, and
versionned (with an outdated version).

The issue was that we had:
- `dune` building Catala
- Makefiles calling `catala` to build and copy the `french_law/ocaml/law_source`
  files
- then `dune` again to build `french_law`

The result was that `dune build` (without running `make` first) would
return a weird error. Also, it's better to avoid versionning artifacts
when we can.

The proposed solution adds ad-hoc dune rules to call the catala
binary, so that it can handle the whole pipeline correctly. If OCaml
is purely a backend, though, a simpler solution that makes us less
dependent on dune would be to handle the compilation of `french_law`
manually.

dune

@@ -1,6 +1,6 @@
-(dirs runtimes compiler french_law build_system)
+(dirs runtimes compiler french_law build_system examples)
 
-(data_only_dirs tests examples syntax_highlighting)
+(data_only_dirs tests syntax_highlighting)
 
 (alias
  (name exec)

examples/aides_logement/dune

@@ -0,0 +1,11 @@
+(rule
+ (targets aides_logement.ml aides_logement_api_web.ml)
+ (deps
+  (source_tree ..))
+ (action
+  (run
+   catala
+   jsoo
+   -t
+   --plugin-dir=../../compiler/plugins
+   aides_logement.catala_fr)))

examples/allocations_familiales/dune

@@ -0,0 +1,11 @@
+(rule
+ (targets allocations_familiales.ml allocations_familiales_api_web.ml)
+ (deps
+  (source_tree ..))
+ (action
+  (run
+   catala
+   jsoo
+   -t
+   --plugin-dir=../../compiler/plugins
+   allocations_familiales.catala_fr)))

examples/allocations_familiales/tests/dune

@@ -0,0 +1,6 @@
+(rule
+ (targets tests_allocations_familiales.ml)
+ (deps
+  (source_tree .))
+ (action
+  (run catala OCaml -t tests_allocations_familiales.catala_fr)))

french_law/ocaml/law_source/.ocamlformat_ignore

@@ -0,0 +1 @@
+*