Fix ArgIterator::GetNextOffset for macOS arm64 (#48632)

* Fix ArgIterator::GetNextOffset for macOS arm64

The ArgIterator::GetNextOffset method was not aligning offsets it returns
for reference types and some others. That was causing coreclr test failures
with GCStress mode 3.

This change fixes it by properly aligning the returned offsets.

* Fix indentation

src/coreclr/vm/callingconvention.h

@@ -1437,7 +1437,8 @@ int ArgIteratorTemplate<ARGITERATOR_BASE>::GetNextOffset()
         break;
     }
     const bool isValueType = (argType == ELEMENT_TYPE_VALUETYPE);
-    const int cbArg = StackElemSize(argSize, isValueType, thValueType.IsFloatHfa());
+    const bool isFloatHfa = thValueType.IsFloatHfa();
+    const int cbArg = StackElemSize(argSize, isValueType, isFloatHfa);
     if (cFPRegs>0 && !this->IsVarArg())
     {
         if (cFPRegs + m_idxFPReg <= 8)
@@ -1495,6 +1496,24 @@ int ArgIteratorTemplate<ARGITERATOR_BASE>::GetNextOffset()
         }
     }
 
+#ifdef OSX_ARM64_ABI
+    int alignment;
+    if (!isValueType)
+    {
+        _ASSERTE((cbArg & (cbArg - 1)) == 0);
+        alignment = cbArg;
+    }
+    else if (isFloatHfa)
+    {
+        alignment = 4;
+    }
+    else
+    {
+        alignment = 8;
+    }
+    m_ofsStack = (int)ALIGN_UP(m_ofsStack, alignment);
+#endif // OSX_ARM64_ABI
+
     int argOfs = TransitionBlock::GetOffsetOfArgs() + m_ofsStack;
     m_ofsStack += cbArg;
     return argOfs;