Invariant: prevent a deleted account from leaving (most) artifacts on the ledger. (#4663)

* Add feature / amendment "InvariantsV1_1"

* Adds invariant AccountRootsDeletedClean:

* Checks that a deleted account doesn't leave any directly
  accessible artifacts behind.
* Always tests, but only changes the transaction result if
  featureInvariantsV1_1 is enabled.
* Unit tests.

* Resolves #4638

* [FOLD] Review feedback from @gregtatcam:

* Fix unused variable warning
* Improve Invariant test const correctness

* [FOLD] Review feedback from @mvadari:

* Centralize the account keylet function list, and some optimization

* [FOLD] Some structured binding doesn't work in clang

* [FOLD] Review feedback 2 from @mvadari:

* Clean up and clarify some comments.

* [FOLD] Change InvariantsV1_1 to unsupported

* Will allow multiple PRs to be merged over time using the same amendment.

* fixup! [FOLD] Change InvariantsV1_1 to unsupported

* [FOLD] Update and clarify some comments. No code changes.

* Move CMake directory

* Rearrange sources

* Rewrite includes

* Recompute loops

* Fix merge issue and formatting

---------

Co-authored-by: Pretty Printer <cpp@ripple.com>

include/xrpl/protocol/Indexes.h

@@ -29,6 +29,7 @@
 #include <xrpl/protocol/STXChainBridge.h>
 #include <xrpl/protocol/Serializer.h>
 #include <xrpl/protocol/UintTypes.h>
+#include <xrpl/protocol/jss.h>
 #include <cstdint>
 
 namespace ripple {
@@ -306,6 +307,26 @@ getTicketIndex(AccountID const& account, std::uint32_t uSequence);
 uint256
 getTicketIndex(AccountID const& account, SeqProxy ticketSeq);
 
+template <class... keyletParams>
+struct keyletDesc
+{
+    std::function<Keylet(keyletParams...)> function;
+    Json::StaticString expectedLEName;
+    bool includeInTests;
+};
+
+// This list should include all of the keylet functions that take a single
+// AccountID parameter.
+std::array<keyletDesc<AccountID const&>, 6> const directAccountKeylets{
+    {{&keylet::account, jss::AccountRoot, false},
+     {&keylet::ownerDir, jss::DirectoryNode, true},
+     {&keylet::signers, jss::SignerList, true},
+     // It's normally impossible to create an item at nftpage_min, but
+     // test it anyway, since the invariant checks for it.
+     {&keylet::nftpage_min, jss::NFTokenPage, true},
+     {&keylet::nftpage_max, jss::NFTokenPage, true},
+     {&keylet::did, jss::DID, true}}};
+
 }  // namespace ripple
 
 #endif