Address my review feedback on (#6017)

- Shortcut on issuer match in canTransfer.
- An asset can transfer if either trustline enabled rippling, so both
  must have it disabled for the transfer to fail with terNO_RIPPLE.
- Remove unnecessary asfDefaultRipple sets in unit tests.
- Add a new unit test helper class: testline, and a macro: THISLINE.
  When included as a parameter to Env::operator(), will include the line
  number of the transaction that didn't get the expected result. Works
  similarly to BEAST_EXPECT. I didn't do the same for the file name,
  because that can be deduced from the testcase name.

src/libxrpl/ledger/View.cpp

@@ -3288,11 +3288,11 @@ canTransfer(
         return tesSUCCESS;
 
     auto const issuerId = issue.getIssuer();
+    if (issuerId == from || issuerId == to)
+        return tesSUCCESS;
     auto const sleIssuer = view.read(keylet::account(issuerId));
     if (sleIssuer == nullptr)
         return tefINTERNAL;  // LCOV_EXCL_LINE
-    if (issuerId == from || issuerId == to)
-        return tesSUCCESS;
 
     auto const isRippleDisabled = [&](AccountID account) -> bool {
         // Line might not exist, but some transfers can create it. If this
@@ -3306,8 +3306,8 @@ canTransfer(
         return sleIssuer->isFlag(lsfDefaultRipple) == false;
     };
 
-    // Fail if rippling disabled on either trust line
-    if (isRippleDisabled(from) || isRippleDisabled(to))
+    // Fail if rippling disabled on both trust lines
+    if (isRippleDisabled(from) && isRippleDisabled(to))
         return terNO_RIPPLE;
 
     return tesSUCCESS;