[Feat] (DirectVulkan, MG_Util): honour a glVertexAttribDivisor other than 1

Vulkan's VK_VERTEX_INPUT_RATE_INSTANCE advances an attribute once per instance and has
no way to say anything else, so every non-zero divisor collapsed to 1: an attribute the
application asked to change every three instances changed every one, and
KHR-GL40.draw_indirect.basic-drawArrays-instancing and its elements sibling drew the
wrong colours from instance one onward.

VK_EXT_vertex_attribute_divisor is exactly this state, so it is enabled when the device
has it and the per-binding divisors ride into the pipeline through
VkPipelineVertexInputDivisorStateCreateInfoEXT. Only divisors other than 1 are listed -
1 is what the plain input rate already means - and they join the layout hash, so two
layouts that differ only in a divisor no longer share a pipeline.

POST reports the feature either way, because without it the failure is silent and looks
like a shader bug: the attribute is fetched, just from the wrong instance. The GLES side
gains the two checks this session's other work made load-bearing for the same reason -
glPatchParameteri (without it GL_PATCH_VERTICES stays at the driver's 3 and a patch draw
of any other size renders nothing) and the transform feedback object entry points
(without them a second object cannot open a capture while the first is paused).

KHR-GL40.draw_indirect on Magma: 70/70 but for the arbitrary primitive-restart index,
which Vulkan cannot express at all.

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.h

@@ -494,6 +494,9 @@ namespace MobileGL::MG_Backend::DirectVulkan {
 
         // VK_EXT_transform_feedback (GL transform feedback capture)
         Bool m_transformFeedbackFeatureEnabled = false;
+        // VK_EXT_vertex_attribute_divisor: without it every non-zero glVertexAttribDivisor
+        // behaves as 1, because that is all Vulkan's instance input rate can express.
+        Bool m_vertexAttributeDivisorEnabled = false;
         static inline PFN_vkCmdBindTransformFeedbackBuffersEXT s_vkCmdBindTransformFeedbackBuffersEXT = nullptr;
         static inline PFN_vkCmdBeginTransformFeedbackEXT s_vkCmdBeginTransformFeedbackEXT = nullptr;
         static inline PFN_vkCmdEndTransformFeedbackEXT s_vkCmdEndTransformFeedbackEXT = nullptr;