Merge bitcoin/bitcoin#24640: Bugfix: RPC/blockchain: Correct description of getblockchaininfo's pruneheight result

06822f8 Bugfix: RPC/blockchain: Correct description of getblockchaininfo's pruneheight result (Luke Dashjr)

Pull request description:

  It is possible that lower blocks are complete due to being stored in the same file as blocks not yet eligible for pruning.

  Not really satisfied with this new description, so suggestions for better phasing welcome :)

  (Split out of #24629)

ACKs for top commit:
  theStack:
    Code-review ACK 06822f8

Tree-SHA512: 755a5a40d065ad77f4ac2c19c0b3502eceb3162034823ee7ce1668100d97e8a2bfb822ac381feb7afd13e653cd08a81d5fa505575531757457d6d22c909a6510

Author: MacroFake

src/rpc/blockchain.cpp

@@ -1178,7 +1178,7 @@ RPCHelpMan getblockchaininfo()
                 {RPCResult::Type::STR_HEX, "chainwork", "total amount of work in active chain, in hexadecimal"},
                 {RPCResult::Type::NUM, "size_on_disk", "the estimated size of the block and undo files on disk"},
                 {RPCResult::Type::BOOL, "pruned", "if the blocks are subject to pruning"},
-                {RPCResult::Type::NUM, "pruneheight", /*optional=*/true, "lowest-height complete block stored (only present if pruning is enabled)"},
+                {RPCResult::Type::NUM, "pruneheight", /*optional=*/true, "height of the last block pruned, plus one (only present if pruning is enabled)"},
                 {RPCResult::Type::BOOL, "automatic_pruning", /*optional=*/true, "whether automatic pruning is enabled (only present if pruning is enabled)"},
                 {RPCResult::Type::NUM, "prune_target_size", /*optional=*/true, "the target size used by pruning (only present if automatic pruning is enabled)"},
                 {RPCResult::Type::OBJ_DYN, "softforks", /*optional=*/true, "(DEPRECATED, returned only if config option -deprecatedrpc=softforks is passed) status of softforks",