Convert Loans to track management fee and use updated rounding

- Move management fee calculations out of transactors an into the
  appropriate functions in LendingHelpers.h.
- Rewrite how overpayments are handled. May changed based on numerical
  analysis.
- Update, fix, and clean up unit tests. Includes adding tolerances for
  some checks where an exact match is unlikely.
- Add "integral()" function to Asset to simplify a common check.

include/xrpl/protocol/Asset.h

@@ -103,6 +103,12 @@ public:
         return holds<Issue>() && get<Issue>().native();
     }
 
+    bool
+    integral() const
+    {
+        return !holds<Issue>() || get<Issue>().native();
+    }
+
     friend constexpr bool
     operator==(Asset const& lhs, Asset const& rhs);
 

include/xrpl/protocol/detail/ledger_entries.macro

@@ -578,10 +578,10 @@ LEDGER_ENTRY(ltLOAN, 0x0089, Loan, loan, ({
     // - PrincipalOutstanding: The rounded portion of the
     //   TotalValueOutstanding that is from the principal borrowed.
     //
-    // - InterestOwed: The rounded portion of the TotalValueOutstanding that
-    //   represents interest specifically owed to the vault. This may be less
-    //   than the interest owed by the borrower, because it excludes the
-    //   expected value of broker management fees.
+    // - ManagementFeeOutstanding: The rounded portion of the
+    //   TotalValueOutstanding that represents management fees
+    //   specifically owed to the broker based on the initial
+    //   loan parameters.
     //
     // There are additional values that can be computed from these:
     //
@@ -589,9 +589,9 @@ LEDGER_ENTRY(ltLOAN, 0x0089, Loan, loan, ({
     //   The total amount of interest still pending on the loan,
     //   independent of management fees.
     //
-    // - ManagementFeeOwed = InterestOutstanding - InterestOwed
-    //   The amount of the total interest that will be sent to the
-    //   broker as management fees.
+    // - InterestOwedToVault = InterestOutstanding - ManagementFeeOutstanding
+    //   The amount of the total interest that is owed to the vault, and
+    //   will be sent to as part of a payment.
     //
     // - TrueTotalLoanValue = PaymentRemaining * PeriodicPayment
     //   The unrounded true total value of the loan.
@@ -603,18 +603,23 @@ LEDGER_ENTRY(ltLOAN, 0x0089, Loan, loan, ({
     //      TrueTotalPrincipalOutstanding
     //   The unrounded true total interest remaining.
     //
+    // - TrueTotalManagementFeeOutstanding = TrueTotalInterestOutstanding *
+    //      LoanBroker.ManagementFeeRate
+    //   The unrounded true total fee still owed to the broker.
+    //
     // Note the the "True" values may differ significantly from the tracked
     // rounded values.
-    {sfPaymentRemaining,     soeDEFAULT},
-    {sfPeriodicPayment,      soeREQUIRED},
-    {sfPrincipalOutstanding, soeDEFAULT},
-    {sfTotalValueOutstanding, soeDEFAULT},
-    {sfInterestOwed,         soeDEFAULT},
-    // Based on the original principal borrowed, used for
+    {sfPaymentRemaining,         soeDEFAULT},
+    {sfPeriodicPayment,          soeREQUIRED},
+    {sfPrincipalOutstanding,     soeDEFAULT},
+    {sfTotalValueOutstanding,    soeDEFAULT},
+    {sfManagementFeeOutstanding, soeDEFAULT},
+    // Based on the computed total value at creation, used for
     // rounding calculated values so they are all on a
     // consistent scale - that is, they all have the same
-    // number of decimal places after the decimal point.
-    {sfLoanScale,            soeDEFAULT},
+    // number of digits after the decimal point (excluding
+    // trailing zeros).
+    {sfLoanScale,                soeDEFAULT},
 }))
 
 #undef EXPAND

include/xrpl/protocol/detail/sfields.macro

@@ -241,7 +241,7 @@ TYPED_SFIELD(sfPrincipalOutstanding,     NUMBER,     13)
 TYPED_SFIELD(sfPrincipalRequested,       NUMBER,     14)
 TYPED_SFIELD(sfTotalValueOutstanding,    NUMBER,     15)
 TYPED_SFIELD(sfPeriodicPayment,          NUMBER,     16)
-TYPED_SFIELD(sfInterestOwed,             NUMBER,     17)
+TYPED_SFIELD(sfManagementFeeOutstanding, NUMBER,     17)
 
 // int32
 TYPED_SFIELD(sfLoanScale,                INT32,      1)