[RE] log_ui_draws: bound the capture by cvar, and log the quad's Z

Three changes, each paid for by a measurement that could not be made without it:

* `--ui_draw_capture_frames` / `--ui_draw_capture_max` replace the compiled-in
  3-frame, 20k-draw bounds. A screen that redraws every frame needs 3; finding
  the frames in which a screen is BUILT needs hundreds, and that answer (the
  title screen never rebuilds — it submits the same 11 draws every frame) is
  only reachable by turning the window up.

* the vertex dump prints all three floats. Attribute 0 of a UI quad is
  k_32_32_32_FLOAT, so the stream carries a Z — the game's own layer key, if it
  had one. It does not: every Z is 0.00000, which is what makes submission order
  the whole of the paint order.

* positions print as floats rather than raw words, now that the format is known.

src/xenia/gpu/command_processor.cc

@@ -327,11 +327,15 @@ void CommandProcessor::CaptureUiDrawForRE(
         if (!q) {
           break;
         }
-        uint32_t w0 = be_u32(q), w1 = be_u32(q + 4);
-        float f0, f1;
+        // Three floats, not two: attribute 0 of a UI quad is k_32_32_32_FLOAT,
+        // so the stream carries a Z per vertex — which is the game's own layer
+        // key if it has one, and the whole question this capture is asked.
+        uint32_t w0 = be_u32(q), w1 = be_u32(q + 4), w2 = be_u32(q + 8);
+        float f0, f1, f2;
         std::memcpy(&f0, &w0, 4);
         std::memcpy(&f1, &w1, 4);
-        ui_out << fmt::format(" [{:08X},{:08X}={:.2f},{:.2f}]", w0, w1, f0, f1);
+        std::memcpy(&f2, &w2, 4);
+        ui_out << fmt::format(" [{:.2f},{:.2f},z={:.5f}]", f0, f1, f2);
       }
     }
   }