Change handling declaration export for classes from flow defs to TS defs

Summary:
The diff introduces exporting classes in TS defs using export default syntax. Previously subsequent flow definitions (output produced by flowToFlowDefs):

```js
declare class Foo {}

declare export default typeof Foo;
```

were translated into the following TS definitions:

```js
declare class Foo {}

declare const $$EXPORT_DEFAULT_DECLARATION$$: typeof Foo;
export default $$EXPORT_DEFAULT_DECLARATION$$;
```

This exports constant that is of type Foo which is not the same as exporting typeof class Foo in TS. If there was another file that imported a Foo class and used it as a type, that would produce an error:

```js
import Foo from './foo';

interface Bar {
  values: Array<Foo> // 'Foo' refers to a value, but is being used as a type here.
}

```

The proposed solution is to export default class:

```js
declare class Foo {}
export default Foo;
```

This change is only applied to classes.

## Changelog:
[flow-api-translator] - Changed generated default exports for declaration exports for classes from flow defs to TS defs

Reviewed By: pieterv

Differential Revision: D69050761

fbshipit-source-id: e6cb54b84262ac1d7a64e05e63b54f23947d236c

tools/hermes-parser/js/flow-api-translator/__tests__/flowDefToTSDef/fixtures/export/declare/default/typeof/class/spec.js

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+declare class Foo {}
+declare export default typeof Foo;

tools/hermes-parser/js/flow-api-translator/__tests__/flowDefToTSDef/fixtures/export/declare/default/typeof/class/translate-result.shot

@@ -0,0 +1,17 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`flowDefToTSDef export/declare/default/typeof/class 1`] = `
+"/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ *
+ * @format
+ */
+
+declare class Foo {}
+export default Foo;
+"
+`;

tools/hermes-parser/js/flow-api-translator/src/flowDefToTSDef.js

@@ -1237,6 +1237,38 @@ const getTransforms = (
             // intentional fallthrough to the "default" handling
           }
 
+          case 'TypeofTypeAnnotation': {
+            if (
+              declaration.type === 'TypeofTypeAnnotation' &&
+              declaration.argument.type === 'Identifier'
+            ) {
+              const name = declaration.argument.name;
+              const exportedVar = topScope.set.get(name);
+              if (exportedVar != null && exportedVar.defs.length === 1) {
+                const def = exportedVar.defs[0];
+
+                switch (def.type) {
+                  case 'ClassName': {
+                    return {
+                      type: 'ExportDefaultDeclaration',
+                      declaration: {
+                        type: 'Identifier',
+                        decorators: [],
+                        name,
+                        optional: false,
+                        loc: DUMMY_LOC,
+                      },
+                      exportKind: 'value',
+                      loc: DUMMY_LOC,
+                    };
+                  }
+                }
+              }
+            }
+
+            // intentional fallthrough to the "default" handling
+          }
+
           default: {
             /*
             flow allows syntax like