flambda-backend: Reroute legacy immediate support for jkinds (#1907)

* Change parsetree layouts to strings

* make depend

* Striate jkind annotations from attributes

* Restore check and add test that `type t : unboxed` isn't allowed

* Fix build

* Main changes

* Restore a similar behavior to [legacy_immediate]

(so that we can allow `type t : value` and `type t : immediate`
even in layouts stable)

* Change tests to not use `[@@void]`, `[@@value]`, etc.

* Change tests to use new error message

* Disallow multiple sources of jkind

* Rename `legacy_immediate` to `is_type_decl`

This concept now just exists within `jkind.ml`, so let's name
it with the appropriate implementation detail.

* `make bootstrap`

* Minor changes suggested in review

* More minor changes suggested in review

* More minor changes suggested in review

* Update ocaml/typing/jkind.ml

Co-authored-by: Richard Eisenberg <[email protected]>

* Revert change that I can't explain

* Store both typed/untyped jkind annotation in typedtree, and delete `const_to_user_written_annotation`

* Remove misleading comment

* Add CRs for doubling-down on backward-incompatible change

* Update ocaml/typing/types.mli

Co-authored-by: Richard Eisenberg <[email protected]>

* Make predefs less confusing if printed

* Resolve merge conflicts and fix build

* Remove obviated module

* Add missing case to comment

* Drop the needless is_type_decl param

* Split Location argument into its components

* Remove no-longer-necessary builtin attrs

* make depend

* Layout annotations in untypeast

* Resolve merge conflicts and update whitespace in tests

* Fix merge conflicts

* make {depend,boot,parser}

* Resolve merge conflicts due to squash+merge

* Fix tests broken by error message change

* Resolve merge conflicts in typing-layouts-float64

* make fmt

* Remove test unintentionally added back in the merge

* Collapse *_beta versions of layouts tests with their stable versions now that the error message is the same

* git rm files that I intended to remove in 5b2bd0c

* Suggestion from review

---------

Co-authored-by: Richard Eisenberg <[email protected]>

Author: ncik-roberts

.depend

@@ -1080,6 +1080,7 @@ typing/includemod_errorprinter.cmi : \
     typing/includemod.cmi
 typing/jkind.cmo : \
     typing/path.cmi \
+    parsing/parsetree.cmi \
     utils/misc.cmi \
     parsing/location.cmi \
     utils/language_extension.cmi \
@@ -1090,6 +1091,7 @@ typing/jkind.cmo : \
     typing/jkind.cmi
 typing/jkind.cmx : \
     typing/path.cmx \
+    parsing/parsetree.cmi \
     utils/misc.cmx \
     parsing/location.cmx \
     utils/language_extension.cmx \
@@ -1103,8 +1105,7 @@ typing/jkind.cmi : \
     parsing/parsetree.cmi \
     parsing/location.cmi \
     parsing/jane_asttypes.cmi \
-    typing/ident.cmi \
-    parsing/builtin_attributes.cmi
+    typing/ident.cmi
 typing/mode.cmo : \
     utils/misc.cmi \
     typing/mode.cmi
@@ -1148,17 +1149,20 @@ typing/oprint.cmo : \
     parsing/printast.cmi \
     typing/outcometree.cmi \
     utils/language_extension.cmi \
+    typing/jkind.cmi \
     parsing/asttypes.cmi \
     typing/oprint.cmi
 typing/oprint.cmx : \
     parsing/printast.cmx \
     typing/outcometree.cmi \
     utils/language_extension.cmx \
+    typing/jkind.cmx \
     parsing/asttypes.cmi \
     typing/oprint.cmi
 typing/oprint.cmi : \
     typing/outcometree.cmi
 typing/outcometree.cmi : \
+    typing/jkind.cmi \
     parsing/asttypes.cmi
 typing/parmatch.cmo : \
     utils/warnings.cmi \
@@ -1222,6 +1226,7 @@ typing/patterns.cmo : \
     typing/mode.cmi \
     parsing/longident.cmi \
     parsing/location.cmi \
+    typing/jkind.cmi \
     typing/ident.cmi \
     typing/env.cmi \
     typing/ctype.cmi \
@@ -1233,6 +1238,7 @@ typing/patterns.cmx : \
     typing/mode.cmx \
     parsing/longident.cmx \
     parsing/location.cmx \
+    typing/jkind.cmx \
     typing/ident.cmx \
     typing/env.cmx \
     typing/ctype.cmx \
@@ -1243,6 +1249,7 @@ typing/patterns.cmi : \
     typing/typedtree.cmi \
     typing/mode.cmi \
     parsing/longident.cmi \
+    typing/jkind.cmi \
     typing/ident.cmi \
     parsing/asttypes.cmi
 typing/persistent_env.cmo : \
@@ -1284,6 +1291,7 @@ typing/predef.cmo : \
     parsing/parsetree.cmi \
     parsing/location.cmi \
     typing/jkind.cmi \
+    parsing/jane_asttypes.cmi \
     typing/ident.cmi \
     typing/btype.cmi \
     parsing/asttypes.cmi \
@@ -1295,6 +1303,7 @@ typing/predef.cmx : \
     parsing/parsetree.cmi \
     parsing/location.cmx \
     typing/jkind.cmx \
+    parsing/jane_asttypes.cmx \
     typing/ident.cmx \
     typing/btype.cmx \
     parsing/asttypes.cmi \
@@ -1362,7 +1371,6 @@ typing/printtyp.cmo : \
     typing/ctype.cmi \
     utils/compilation_unit.cmi \
     utils/clflags.cmi \
-    parsing/builtin_attributes.cmi \
     typing/btype.cmi \
     parsing/asttypes.cmi \
     typing/printtyp.cmi
@@ -1388,7 +1396,6 @@ typing/printtyp.cmx : \
     typing/ctype.cmx \
     utils/compilation_unit.cmx \
     utils/clflags.cmx \
-    parsing/builtin_attributes.cmx \
     typing/btype.cmx \
     parsing/asttypes.cmi \
     typing/printtyp.cmi
@@ -1933,6 +1940,7 @@ typing/typedtree.cmo : \
     parsing/longident.cmi \
     parsing/location.cmi \
     typing/jkind.cmi \
+    parsing/jane_asttypes.cmi \
     typing/ident.cmi \
     typing/env.cmi \
     parsing/asttypes.cmi \
@@ -1948,6 +1956,7 @@ typing/typedtree.cmx : \
     parsing/longident.cmx \
     parsing/location.cmx \
     typing/jkind.cmx \
+    parsing/jane_asttypes.cmx \
     typing/ident.cmx \
     typing/env.cmx \
     parsing/asttypes.cmi \
@@ -1963,6 +1972,7 @@ typing/typedtree.cmi : \
     parsing/longident.cmi \
     parsing/location.cmi \
     typing/jkind.cmi \
+    parsing/jane_asttypes.cmi \
     typing/ident.cmi \
     typing/env.cmi \
     parsing/asttypes.cmi