[Vulkan] Add resolution scaling support to Vulkan backend.

Largely similar to D3D12 implementation but more simple buffer
management and no mips scaling. Includes both FBO and FSI
rendering paths.

Tested on Linux with 2x2 and 3x3 running smoothly.

src/xenia/gpu/spirv_shader_translator_memexport.cc

@@ -30,10 +30,70 @@ void SpirvShaderTranslator::ExportToMemory(uint8_t export_eM) {
 
   // Check if memory export is allowed in this guest shader invocation.
   std::optional<SpirvBuilder::IfBuilder> if_memexport_allowed;
-  if (main_memexport_allowed_ != spv::NoResult) {
-    if_memexport_allowed.emplace(main_memexport_allowed_,
-                                 spv::SelectionControlDontFlattenMask,
-                                 *builder_);
+  spv::Id memexport_allowed = main_memexport_allowed_;
+
+  // For pixel shaders with resolution scaling, only allow memory export from
+  // the center host pixel to avoid duplicate exports.
+  if (is_pixel_shader() &&
+      (draw_resolution_scale_x_ > 1 || draw_resolution_scale_y_ > 1)) {
+    assert_true(input_fragment_coordinates_ != spv::NoResult);
+
+    // Check if we're at the center pixel (scale/2 for both X and Y).
+    spv::Id is_center_pixel = builder_->makeBoolConstant(true);
+
+    // Check X coordinate.
+    if (draw_resolution_scale_x_ > 1) {
+      id_vector_temp_.clear();
+      id_vector_temp_.push_back(const_int_0_);
+      spv::Id pixel_x = builder_->createUnaryOp(
+          spv::OpConvertFToU, type_uint_,
+          builder_->createLoad(
+              builder_->createAccessChain(spv::StorageClassInput,
+                                          input_fragment_coordinates_,
+                                          id_vector_temp_),
+              spv::NoPrecision));
+      spv::Id pixel_x_remainder = builder_->createBinOp(
+          spv::OpUMod, type_uint_, pixel_x,
+          builder_->makeUintConstant(draw_resolution_scale_x_));
+      is_center_pixel = builder_->createBinOp(
+          spv::OpLogicalAnd, type_bool_, is_center_pixel,
+          builder_->createBinOp(
+              spv::OpIEqual, type_bool_, pixel_x_remainder,
+              builder_->makeUintConstant(draw_resolution_scale_x_ >> 1)));
+    }
+
+    // Check Y coordinate.
+    if (draw_resolution_scale_y_ > 1) {
+      id_vector_temp_.clear();
+      id_vector_temp_.push_back(builder_->makeIntConstant(1));
+      spv::Id pixel_y = builder_->createUnaryOp(
+          spv::OpConvertFToU, type_uint_,
+          builder_->createLoad(
+              builder_->createAccessChain(spv::StorageClassInput,
+                                          input_fragment_coordinates_,
+                                          id_vector_temp_),
+              spv::NoPrecision));
+      spv::Id pixel_y_remainder = builder_->createBinOp(
+          spv::OpUMod, type_uint_, pixel_y,
+          builder_->makeUintConstant(draw_resolution_scale_y_));
+      is_center_pixel = builder_->createBinOp(
+          spv::OpLogicalAnd, type_bool_, is_center_pixel,
+          builder_->createBinOp(
+              spv::OpIEqual, type_bool_, pixel_y_remainder,
+              builder_->makeUintConstant(draw_resolution_scale_y_ >> 1)));
+    }
+
+    // Combine with existing memexport_allowed condition.
+    memexport_allowed =
+        memexport_allowed != spv::NoResult
+            ? builder_->createBinOp(spv::OpLogicalAnd, type_bool_,
+                                    memexport_allowed, is_center_pixel)
+            : is_center_pixel;
+  }
+
+  if (memexport_allowed != spv::NoResult) {
+    if_memexport_allowed.emplace(
+        memexport_allowed, spv::SelectionControlDontFlattenMask, *builder_);
   }
 
   // If the pixel was killed (but the actual killing on the SPIR-V side has not