[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_Util/Converters/MGToVk/RenderStateEnumConverter.cpp

@@ -25,6 +25,11 @@ namespace MobileGL {
             case GL_TRIANGLE_FAN:
                 return VK_PRIMITIVE_TOPOLOGY_TRIANGLE_FAN;
             case GL_LINE_LOOP:
+                // DrawArrays/DrawElements rewrite line loops into closed indexed
+                // strips; entry points without that rewrite (instanced/indirect)
+                // degrade to an open strip, which only misses the closing segment.
+                MGLOG_W("GL_LINE_LOOP without index rewrite; drawing as LINE_STRIP");
+                return VK_PRIMITIVE_TOPOLOGY_LINE_STRIP;
             default:
                 MGLOG_W("Unrecognized primitive topology");
                 return VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST;