[crypto] add new flavors of 'Update()' for SHA-256 and HMAC computation (#6002)

This commit updates `Sha256` and `HmacSha256` classes adding new
flavors of `Update()` method which inputs bytes from a given buffer,
or from an object, or read from a `Message` for hash calculation.

This commit also updates unit test to add more test-cases (from RFC
4231) for HMAC and adds new set of test-cases for SHA-256. The test
also covers calculating hash over data read directly from a `Message`.

tests/unit/test_ecdsa.cpp

@@ -101,7 +101,7 @@ void TestEcdsaVector(void)
 
     printf("\nHash the message ----------------------------------------------------------\n");
     sha256.Start();
-    sha256.Update(kMessage, sizeof(kMessage));
+    sha256.Update(kMessage);
     sha256.Finish(hash);
 
     DumpBuffer("Hash", hash.GetBytes(), sizeof(hash));
@@ -153,7 +153,7 @@ void TestEdsaKeyGenerationSignAndVerify(void)
 
     printf("\nHash the message ----------------------------------------------------------\n");
     sha256.Start();
-    sha256.Update(reinterpret_cast<const uint8_t *>(kMessage), sizeof(kMessage) - 1);
+    sha256.Update(kMessage, sizeof(kMessage) - 1);
     sha256.Finish(hash);
 
     DumpBuffer("Hash", hash.GetBytes(), sizeof(hash));
@@ -167,7 +167,7 @@ void TestEdsaKeyGenerationSignAndVerify(void)
     printf("\nSignature was verified successfully.");
 
     sha256.Start();
-    sha256.Update(reinterpret_cast<const uint8_t *>(kMessage), sizeof(kMessage)); // include null char
+    sha256.Update(kMessage, sizeof(kMessage)); // include null char
     sha256.Finish(hash);
     VerifyOrQuit(publicKey.Verify(hash, signature) != OT_ERROR_NONE,
                  "PublicKey::Verify() passed for invalid signature");