add sample zero cost variant version of docgen representation

Author: zth

tools/src/Tools_Docgen2.res

@@ -0,0 +1,54 @@
+type recordField = {
+  name: string,
+  deprecated?: string,
+  optional: bool,
+  docstrings: array<string>,
+  signature: string,
+}
+
+type constructor = {
+  name: string,
+  deprecated?: string,
+  optional: bool,
+  docstrings: array<string>,
+  signature: string,
+}
+
+@tag("kind")
+type typeDetail =
+  | @as("record") Record({items: array<recordField>})
+  | @as("variant") Variant({items: array<constructor>})
+
+@tag("kind")
+type rec docItem =
+  | @as("value")
+  Value({
+      id: string,
+      name: string,
+      deprecated?: string,
+      signature: string,
+      docstrings: array<string>,
+    })
+  | @as("type")
+  Type({
+      id: string,
+      name: string,
+      deprecated?: string,
+      signature: string,
+      detail?: typeDetail,
+    })
+  | @as("module") Module({id: string, name: string, items: array<docItem>})
+  | @as("moduleAlias")
+  ModuleAlias({
+      id: string,
+      name: string,
+      docstrings: array<string>,
+      items: array<docItem>,
+    })
+
+type docsForModule = {
+  name: string,
+  deprecated?: string,
+  docstrings: array<string>,
+  items: array<docItem>,
+}