Introduce AMM support (XLS-30d): (#4294)

Add AMM functionality:
- InstanceCreate
- Deposit
- Withdraw
- Governance
- Auctioning
- payment engine integration

To support this functionality, add:
- New RPC method, `amm_info`, to fetch pool and LPT balances
- AMM Root Account
- trust line for each IOU AMM token
- trust line to track Liquidity Provider Tokens (LPT)
- `ltAMM` object

The `ltAMM` object tracks:
- fee votes
- auction slot bids
- AMM tokens pair
- total outstanding tokens balance
- `AMMID` to AMM `RootAccountID` mapping

Add new classes to facilitate AMM integration into the payment engine.
`BookStep` uses these classes to infer if AMM liquidity can be consumed.

The AMM formula implementation uses the new Number class added in #4192.
IOUAmount and STAmount use Number arithmetic.

Add AMM unit tests for all features.

AMM requires the following amendments:
- featureAMM
- fixUniversalNumber
- featureFlowCross

Notes:
- Current trading fee threshold is 1%
- AMM currency is generated by: 0x03 + 152 bits of sha256{cur1, cur2}
- Current max AMM Offers is 30

---------

Co-authored-by: Howard Hinnant <howard.hinnant@gmail.com>

src/test/app/PayStrand_test.cpp

@@ -26,8 +26,10 @@
 #include <ripple/ledger/Sandbox.h>
 #include <ripple/protocol/Feature.h>
 #include <ripple/protocol/jss.h>
+#include "ripple/app/paths/AMMContext.h"
 #include <test/jtx.h>
 #include <test/jtx/PathSet.h>
+#include <test/jtx/TestHelpers.h>
 
 namespace ripple {
 namespace test {
@@ -162,26 +164,6 @@ iape(AccountID const& account)
         STPathElement::typeIssuer, xrpAccount(), xrpCurrency(), account);
 };
 
-// Currency path element
-STPathElement
-cpe(Currency const& c)
-{
-    return STPathElement(
-        STPathElement::typeCurrency, xrpAccount(), c, xrpAccount());
-};
-
-// All path element
-STPathElement
-allpe(AccountID const& a, Issue const& iss)
-{
-    return STPathElement(
-        STPathElement::typeAccount | STPathElement::typeCurrency |
-            STPathElement::typeIssuer,
-        a,
-        iss.currency,
-        iss.account);
-};
-
 class ElementComboIter
 {
     enum class SB /*state bit*/
@@ -657,6 +639,8 @@ struct PayStrand_test : public beast::unit_test::suite
         using B = ripple::Book;
         using XRPS = XRPEndpointStepInfo;
 
+        AMMContext ammContext(alice, false);
+
         auto test = [&, this](
                         jtx::Env& env,
                         Issue const& deliver,
@@ -674,6 +658,7 @@ struct PayStrand_test : public beast::unit_test::suite
                 path,
                 true,
                 false,
+                ammContext,
                 env.app().logs().journal("Flow"));
             BEAST_EXPECT(ter == expTer);
             if (sizeof...(expSteps) != 0)
@@ -701,6 +686,7 @@ struct PayStrand_test : public beast::unit_test::suite
                     path,
                     true,
                     false,
+                    ammContext,
                     env.app().logs().journal("Flow"));
                 (void)_;
                 BEAST_EXPECT(ter == tesSUCCESS);
@@ -717,6 +703,7 @@ struct PayStrand_test : public beast::unit_test::suite
                     path,
                     true,
                     false,
+                    ammContext,
                     env.app().logs().journal("Flow"));
                 (void)_;
                 BEAST_EXPECT(ter == tesSUCCESS);
@@ -836,6 +823,7 @@ struct PayStrand_test : public beast::unit_test::suite
                         STPath(),
                         true,
                         false,
+                        ammContext,
                         flowJournal);
                     BEAST_EXPECT(r.first == temBAD_PATH);
                 }
@@ -851,6 +839,7 @@ struct PayStrand_test : public beast::unit_test::suite
                         STPath(),
                         true,
                         false,
+                        ammContext,
                         flowJournal);
                     BEAST_EXPECT(r.first == temBAD_PATH);
                 }
@@ -866,6 +855,7 @@ struct PayStrand_test : public beast::unit_test::suite
                         STPath(),
                         true,
                         false,
+                        ammContext,
                         flowJournal);
                     BEAST_EXPECT(r.first == temBAD_PATH);
                 }
@@ -1002,6 +992,7 @@ struct PayStrand_test : public beast::unit_test::suite
                 STPath(),
                 true,
                 false,
+                ammContext,
                 env.app().logs().journal("Flow"));
             BEAST_EXPECT(ter == tesSUCCESS);
             BEAST_EXPECT(equal(strand, D{alice, gw, usdC}));
@@ -1028,6 +1019,7 @@ struct PayStrand_test : public beast::unit_test::suite
                 path,
                 false,
                 false,
+                ammContext,
                 env.app().logs().journal("Flow"));
             BEAST_EXPECT(ter == tesSUCCESS);
             BEAST_EXPECT(equal(