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/Feature.h

@@ -80,7 +80,7 @@ namespace detail {
 // Feature.cpp. Because it's only used to reserve storage, and determine how
 // large to make the FeatureBitset, it MAY be larger. It MUST NOT be less than
 // the actual number of amendments. A LogicError on startup will verify this.
-static constexpr std::size_t numFeatures = 77;
+static constexpr std::size_t numFeatures = 78;
 
 /** Amendments that this server supports and the default voting behavior.
    Whether they are enabled depends on the Rules defined in the validated
@@ -370,6 +370,7 @@ extern uint256 const featureNFTokenMintOffer;
 extern uint256 const fixReducedOffersV2;
 extern uint256 const fixEnforceNFTokenTrustline;
 extern uint256 const fixInnerObjTemplate2;
+extern uint256 const featureInvariantsV1_1;
 
 }  // namespace ripple