Merge bitcoin#24564: doc: Clarify that CheckSequenceLocksAtTip is a validation function

fa86710 Clarify that CheckSequenceLocksAtTip is a validation function (MarcoFalke)

Pull request description:

  It has been pointed out that a bug in this function can prevent block template creation. ( bitcoin#24080 (comment) ) So it seems that the scope of this function is more than "policy". Rename it back to "validation", to partially revert commit fa4e30b.

ACKs for top commit:
  ajtowns:
    ACK fa86710 - looks fine to me
  glozow:
    ACK fa86710

Tree-SHA512: 2e0df8c70df4cbea857977f140a8616cfa7505e74df66c9c9fbcf184670ce3ce7567183c3f76e6f3fe8ca6de0e065b9babde6352d6cb495e71ea077ddedbc3f4

Author: glozow

src/validation.h

@@ -256,7 +256,7 @@ PackageMempoolAcceptResult ProcessNewPackage(CChainState& active_chainstate, CTx
                                                    const Package& txns, bool test_accept)
                                                    EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
-/* Transaction policy functions */
+/* Mempool validation helper functions */
 
 /**
  * Check if transaction will be final in the next block to be created.