[Feat] (DirectVulkan): emulate GL_LINE_LOOP with closed indexed line strips

Vulkan has no LINE_LOOP topology and the frontend used to reject the mode
with GL_INVALID_OPERATION, which is itself non-conformant (several KHR-GL33
transform_feedback tests draw line loops and expect no error). DrawArrays,
DrawElements and DrawElementsBaseVertex now rewrite the draw into an
indexed GL_LINE_STRIP whose synthesized uint32 index list revisits the
first vertex, delivered through the client-memory index path (a new
forceClientMemory flag keeps a bound element-array buffer from hijacking
the synthesized pointer). Entry points without the rewrite degrade to an
open line strip instead of a triangle list.

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.cpp

@@ -2848,7 +2848,9 @@ void main() {
         }
 
         const Uint8* indexBytes = nullptr;
-        const auto& indexBufferShared = vao.GetIndexBufferBindingSlot().GetBoundObject();
+        const auto& indexBufferShared = indexView.forceClientMemory
+            ? SharedPtr<MG_State::GLState::BufferObject>{}
+            : vao.GetIndexBufferBindingSlot().GetBoundObject();
         if (indexBufferShared != nullptr) {
             const SizeT bufferSize = indexBufferShared->GetSize();
             if (indexBufferShared->MappedData() == nullptr || indexView.indexByteOffset > bufferSize ||
@@ -3262,7 +3264,8 @@ void main() {
             }
         }
 
-        const auto* indexBuffer = vao.GetIndexBufferBindingSlot().GetBoundObject().get();
+        const auto* indexBuffer =
+            pIndexBufferView->forceClientMemory ? nullptr : vao.GetIndexBufferBindingSlot().GetBoundObject().get();
         if (indexBuffer == nullptr) {
             // No element-array buffer: the view's byte offset is a raw client pointer
             // (desktop drivers accept client-memory indices and the GL CTS relies on