[GPU] Add log_draws: dump per-draw vertex declaration for RE

Reverse-engineering aid for decoding game mesh formats against GPU ground
truth. When the `log_draws` cvar is set, each distinct draw's primitive
type, index buffer (guest base / count / format / endianness), and full
per-stream vertex declaration (fetch-constant base + stride, and every
element's format + offset) is written to xenia_re_draws.log.

- command_processor.{h,cc}: CommandProcessor::LogDrawForRE(), no-op unless
  the cvar is set. De-dups by the vertex-declaration fingerprint (shader +
  primitive + element formats/offsets), so animated UI that redraws the
  same format into fresh buffers every frame collapses to one record --
  keeping it near-free (an earlier address-keyed de-dup flooded the log and
  stalled the GPU thread). Capped at 4096 distinct formats.
- pm4_command_processor_implement.h: call it from ExecutePacketType3Draw
  after IssueDraw (so the vertex shader has been analyzed). Backend-agnostic
  base path -- works for the Vulkan build.

Used to confirm Project Sylpheed's XBG7 mesh layout (triangle list, pos
f32x3 / normal f16x4 / uv f16x2, variable stride).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/xenia/gpu/command_processor.h

@@ -446,6 +446,13 @@ class CommandProcessor {
   }
   virtual bool IssueCopy() { return false; }
 
+  // Reverse-engineering aid (cvar `log_draws`): dump the guest's exact
+  // primitive type + index buffer + per-stream vertex declaration for each
+  // distinct draw to a dedicated file, for decoding game mesh formats.
+  // No-op unless the cvar is enabled. Defined in command_processor.cc.
+  void LogDrawForRE(uint32_t vgt_draw_initiator_value,
+                    const IndexBufferInfo* index_buffer_info);
+
   // "Actual" is for the command processor thread, to be read by the
   // implementations.
   SwapPostEffect GetActualSwapPostEffect() const {