[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_fetch.cc

@@ -1066,7 +1066,9 @@ void SpirvShaderTranslator::ProcessTextureFetchInstruction(
       coordinates[coordinate_component_index] = coordinates_operand;
     }
 
-    // TODO(Triang3l): Reverting the resolution scale.
+    // Resolution scale doesn't need reverting for texture weights - weights are
+    // calculated from fractional parts of coordinates which are
+    // scale-independent.
 
     if (instr.opcode == ucode::FetchOpcode::kGetTextureWeights) {
       // FIXME(Triang3l): Filtering modes should possibly be taken into account,