Merge #19004: refactor: Replace const char* to std::string

c57f03ce17 refactor: Replace const char* to std::string (Calvin Kim)

Pull request description:

  Rationale: Addresses #19000
  Some functions should be returning std::string instead of const char*.
  This commit changes that.

  Main benefits/reasoning:

  1.  The functions never return nullptr, so returning a string makes code at call sites easier to review (reviewers don't have to read the source code to verify that a nullptr is never returned)
  2. All call sites convert to string anyway

ACKs for top commit:
  MarcoFalke:
    re-ACK c57f03ce17 (no changes since previous review) 🚃
  Empact:
    Fair enough, Code Review ACK c57f03ce17
  practicalswift:
    ACK c57f03ce17 -- patch looks correct
  hebasto:
    re-ACK c57f03ce17

Tree-SHA512: 9ce99bb38fe399b54844315048204cafce0f27fd8f24cae357fa7ac6f5d8094d57bbf5f5c1f5878a65f2d35e4a3f95d527eb17f49250b690c591c0df86ca84fd

src/script/script.h

@@ -193,7 +193,7 @@ enum opcodetype
 // Maximum value that an opcode can be
 static const unsigned int MAX_OPCODE = OP_NOP10;
 
-const char* GetOpName(opcodetype opcode);
+std::string GetOpName(opcodetype opcode);
 
 class scriptnum_error : public std::runtime_error
 {