cranelift: Add big and little endian memory accesses to interpreter (#5893)

* Added `mem_flags` parameter to `State::checked_{load,store}` as the means
for determining the endianness, typically derived from an instruction.

* Added `native_endianness` property to `InterpreterState` as fallback when
determining endianness, such as in cases where there are no memory flags
avaiable or set.

* Added `to_be` and `to_le` methods to `DataValue`.

* Added `AtomicCas` and `AtomicRmw` to list of instructions with retrievable
memory flags for `InstructionData::memflags`.

* Enabled `atomic-{cas,rmw}-subword-{big,little}.clif` for interpreter run
tests.

cranelift/codegen/src/ir/instructions.rs

@@ -403,7 +403,9 @@ impl InstructionData {
             &InstructionData::Load { flags, .. }
             | &InstructionData::LoadNoOffset { flags, .. }
             | &InstructionData::Store { flags, .. }
-            | &InstructionData::StoreNoOffset { flags, .. } => Some(flags),
+            | &InstructionData::StoreNoOffset { flags, .. }
+            | &InstructionData::AtomicCas { flags, .. }
+            | &InstructionData::AtomicRmw { flags, .. } => Some(flags),
             _ => None,
         }
     }