[flow] abstract get_def_process_location mapper over annot position

Summary:
This diff changes the signature of `get_def_process_location` mapper from a
```
 [ALoc.t, ALoc.t * Type.t, ALoc.t, ALoc.t * Type.t] Flow_polymorphic_ast_mapper.mapper
```
to a
```
[ALoc.t, 'T, ALoc.t, 'T] Typed_ast_finder.enclosing_node_mapper
```
The main change is in the type of the annotation position which is now abstract. For this to work we need to change places that before inspected this position and expected to find an `ALoc.t * Type.t`, to now first call into one of the following (virtual) methods
```
method virtual loc_of_annot : 'T -> ALoc.t
method virtual type_from_enclosing_node : 'T -> Type.t
method virtual get_module_t : 'T -> ALoc.t Ast.StringLiteral.t -> Type.t
method virtual remote_name_def_loc_of_import_named_specifier: (ALoc.t, 'T) Ast.Statement.ImportDeclaration.named_specifier -> ALoc.t option
method virtual remote_default_name_def_loc_of_import_declaration: 'T -> ALoc.t * (ALoc.t, 'T) Ast.Statement.ImportDeclaration.t -> ALoc.t option
method virtual component_name_of_jsx_element: 'T -> (ALoc.t, 'T) Ast.JSX.element -> ALoc.t * Type.t
```
Each class that finalizes `searcher`, will need to implement these methods. `typed_ast_searcher` which is included in this diff restores the behavior of `searcher` before this change. All these operations can be implemented by looking up relevant information in the typed AST.

Follow up diffs implement a searcher that create typed AST nodes on-demand, by calling facilities introduced in the previous diff.

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D55053045

fbshipit-source-id: c52b0ea1eb90e9a4c86374970787cc7c60946ea6

src/parser_utils/ast_loc_utils.ml

@@ -15,3 +15,13 @@ let loc_to_aloc_mapper : (Loc.t, Loc.t, ALoc.t, ALoc.t) Flow_polymorphic_ast_map
 
     method on_type_annot = ALoc.of_loc
   end
+
+let loc_to_aloc_unit_mapper :
+    (Loc.t, Loc.t, ALoc.t, ALoc.t * unit) Flow_polymorphic_ast_mapper.mapper =
+  object
+    inherit [Loc.t, Loc.t, ALoc.t, ALoc.t * unit] Flow_polymorphic_ast_mapper.mapper
+
+    method on_loc_annot = ALoc.of_loc
+
+    method on_type_annot x = (ALoc.of_loc x, ())
+  end

src/parser_utils/ast_loc_utils.mli

@@ -8,3 +8,6 @@
 (* Converts a (Loc.t, Loc.t) AST into a (ALoc.t, ALoc.t) AST. Leaves the underlying representation
  * of the contained ALoc.ts concrete. *)
 val loc_to_aloc_mapper : (Loc.t, Loc.t, ALoc.t, ALoc.t) Flow_polymorphic_ast_mapper.mapper
+
+val loc_to_aloc_unit_mapper :
+  (Loc.t, Loc.t, ALoc.t, ALoc.t * unit) Flow_polymorphic_ast_mapper.mapper

src/services/get_def/getDef_js.ml

@@ -131,7 +131,7 @@ end
 
 let get_def ~options ~loc_of_aloc ~cx ~file_sig ~ast ~typed_ast ~purpose requested_loc =
   let require_loc_map = File_sig.require_loc_map file_sig in
-  let is_legit_require (source_aloc, _) =
+  let is_legit_require source_aloc =
     let source_loc = loc_of_aloc source_aloc in
     SMap.exists (fun _ locs -> List.exists (fun loc -> loc = source_loc) locs) require_loc_map
   in