gh-136547: fix hashlib_helper for blocking and requesting digests (#136762)

- Fix `hashlib_helper.block_algorithm` where the dummy functions were incorrectly defined.
- Rename `hashlib_helper.HashAPI` to `hashlib_helper.HashInfo` and add more helper methods.
- Simplify `hashlib_helper.requires_*()` functions.
- Rewrite some private helpers in `hashlib_helper`.
- Remove `find_{builtin,openssl}_hashdigest_constructor()` as they are no more needed and were
  not meant to be public in the first place.
- Fix some tests in `test_hashlib` when FIPS mode is on.

Lib/test/test_hashlib.py

@@ -545,13 +545,17 @@ def check(self, name, data, hexdigest, shake=False, **kwargs):
 
     def check_file_digest(self, name, data, hexdigest):
         hexdigest = hexdigest.lower()
-        try:
-            hashlib.new(name)
-        except ValueError:
-            # skip, algorithm is blocked by security policy.
-            return
-        digests = [name]
-        digests.extend(self.constructors_to_test[name])
+        digests = []
+        for digest in [name, *self.constructors_to_test[name]]:
+            try:
+                if callable(digest):
+                    digest(b"")
+                else:
+                    hashlib.new(digest)
+            except ValueError:
+                # skip, algorithm is blocked by security policy.
+                continue
+            digests.append(digest)
 
         with tempfile.TemporaryFile() as f:
             f.write(data)