Miscellaneous refactors and updates (#5590)

- Added a new Invariant: `ValidPseudoAccounts` which checks that all pseudo-accounts behave consistently through creation and updates, and that no "real" accounts look like pseudo-accounts (which means they don't have a 0 sequence). 
- `to_short_string(base_uint)`. Like `to_string`, but only returns the first 8 characters. (Similar to how a git commit ID can be abbreviated.) Used as a wrapped sink to prefix most transaction-related messages. More can be added later.
- `XRPL_ASSERT_PARTS`. Convenience wrapper for `XRPL_ASSERT`, which takes the `function` and `description` as separate parameters.
- `SField::sMD_PseudoAccount`. Metadata option for `SField` definitions to indicate that the field, if set in an `AccountRoot` indicates that account is a pseudo-account. Removes the need for hard-coded field lists all over the place. Added the flag to `AMMID` and `VaultID`.
- Added functionality to `SField` ctor to detect both code and name collisions using asserts. And require all SFields to have a name
- Convenience type aliases `STLedgerEntry::const_pointer` and `STLedgerEntry::const_ref`. (`SLE` is an alias to `STLedgerEntry`.)
- Generalized `feeunit.h` (`TaggedFee`) into `unit.h` (`ValueUnit`) and added new "BIPS"-related tags for future use. Also refactored the type restrictions to use Concepts.
- Restructured `transactions.macro` to do two big things
	1. Include the `#include` directives for transactor header files directly in the macro file. Removes the need to update `applySteps.cpp` and the resulting conflicts.
	2. Added a `privileges` parameter to the `TRANSACTION` macro, which specifies some of the operations a transaction is allowed to do. These `privileges` are enforced by invariant checks. Again, removed the need to update scattered lists of transaction types in various checks.
- Unit tests:
	1.  Moved more helper functions into `TestHelpers.h` and `.cpp`. 
	2. Cleaned up the namespaces to prevent / mitigate random collisions and ambiguous symbols, particularly in unity builds.
	3. Generalized `Env::balance` to add support for `MPTIssue` and `Asset`.
	4. Added a set of helper classes to simplify `Env` transaction parameter classes: `JTxField`, `JTxFieldWrapper`, and a bunch of classes derived or aliased from it. For an example of how awesome it is, check the changes `src/test/jtx/escrow.h` for how much simpler the definitions are for `finish_time`, `cancel_time`, `condition`, and `fulfillment`. 
	5. Generalized several of the amount-related helper classes to understand `Asset`s.
     6. `env.balance` for an MPT issuer will return a negative number (or 0) for consistency with IOUs.

Author: ximinez

include/xrpl/basics/base_uint.h

@@ -632,6 +632,16 @@ to_string(base_uint<Bits, Tag> const& a)
     return strHex(a.cbegin(), a.cend());
 }
 
+template <std::size_t Bits, class Tag>
+inline std::string
+to_short_string(base_uint<Bits, Tag> const& a)
+{
+    static_assert(
+        base_uint<Bits, Tag>::bytes > 4,
+        "For 4 bytes or less, use a native type");
+    return strHex(a.cbegin(), a.cbegin() + 4) + "...";
+}
+
 template <std::size_t Bits, class Tag>
 inline std::ostream&
 operator<<(std::ostream& out, base_uint<Bits, Tag> const& u)

include/xrpl/basics/safe_cast.h

@@ -28,9 +28,8 @@ namespace ripple {
 // the destination can hold all values of the source.  This is particularly
 // handy when the source or destination is an enumeration type.
 
-template <class Dest, class Src>
-static constexpr bool is_safetocasttovalue_v =
-    (std::is_integral_v<Src> && std::is_integral_v<Dest>) &&
+template <class Src, class Dest>
+concept SafeToCast = (std::is_integral_v<Src> && std::is_integral_v<Dest>) &&
     (std::is_signed<Src>::value || std::is_unsigned<Dest>::value) &&
     (std::is_signed<Src>::value != std::is_signed<Dest>::value
          ? sizeof(Dest) > sizeof(Src)
@@ -78,7 +77,7 @@ inline constexpr std::
     unsafe_cast(Src s) noexcept
 {
     static_assert(
-        !is_safetocasttovalue_v<Dest, Src>,
+        !SafeToCast<Src, Dest>,
         "Only unsafe if casting signed to unsigned or "
         "destination is too small");
     return static_cast<Dest>(s);

include/xrpl/beast/utility/instrumentation.h

@@ -39,11 +39,16 @@ OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 #endif
 
 #define XRPL_ASSERT ALWAYS_OR_UNREACHABLE
+#define XRPL_ASSERT_PARTS(cond, function, description, ...) \
+    XRPL_ASSERT(cond, function " : " description)
 
 // How to use the instrumentation macros:
 //
 // * XRPL_ASSERT if cond must be true but the line might not be reached during
 //   fuzzing. Same like `assert` in normal use.
+// * XRPL_ASSERT_PARTS is for convenience, and works like XRPL_ASSERT, but
+//   splits the message param into "function" and "description", then joins
+//   them with " : " before passing to XRPL_ASSERT.
 // * ALWAYS if cond must be true _and_ the line must be reached during fuzzing.
 //   Same like `assert` in normal use.
 // * REACHABLE if the line must be reached during fuzzing

include/xrpl/ledger/View.h

@@ -561,12 +561,28 @@ createPseudoAccount(
 [[nodiscard]] bool
 isPseudoAccount(std::shared_ptr<SLE const> sleAcct);
 
+// Returns the list of fields that define an ACCOUNT_ROOT as a pseudo-account if
+// set
+// Pseudo-account designator fields MUST be maintained by including the
+// SField::sMD_PseudoAccount flag in the SField definition. (Don't forget to
+// "| SField::sMD_Default"!) The fields do NOT need to be amendment-gated,
+// since a non-active amendment will not set any field, by definition.
+// Specific properties of a pseudo-account are NOT checked here, that's what
+// InvariantCheck is for.
+[[nodiscard]] std::vector<SField const*> const&
+getPseudoAccountFields();
+
 [[nodiscard]] inline bool
 isPseudoAccount(ReadView const& view, AccountID accountId)
 {
     return isPseudoAccount(view.read(keylet::account(accountId)));
 }
 
+[[nodiscard]] TER
+canAddHolding(ReadView const& view, Asset const& asset);
+
+/// Any transactors that call addEmptyHolding() in doApply must call
+/// canAddHolding() in preflight with the same View and Asset
 [[nodiscard]] TER
 addEmptyHolding(
     ApplyView& view,