[custom levels] A few bug fixes (#3736)

- Bug fix to KD tree splitting, should fix cases with bad vertex
colors/alphas.
- Normalize normals instead of asserting if they are the wrong length.
**the fact that blender exports normals incorrectly is a bug and I doubt
their implementation is correct if you've scaled things on only on
axis.**
- Automatically resize metallic texture (envmap strength) if it doesn't
match the size of the rgb texture instead of asserting

Co-authored-by: water111 <awaterford1111445@gmail.com>

test/common/test_image_resize.cpp

@@ -0,0 +1,37 @@
+#include <cstdio>
+#include <vector>
+
+#include "common/common_types.h"
+#include "common/util/FileUtil.h"
+#include "common/util/Timer.h"
+#include "common/util/image_resize.h"
+
+int main() {
+  int src_h = 30;
+  int src_w = 30;
+  int check_divide = 3;
+  int dst_sz = 300;
+
+  std::vector<u8> src;
+  for (int h = 0; h < src_h; h++) {
+    for (int w = 0; w < src_w; w++) {
+      u8 color = (((h / check_divide) & 1) ^ ((w / check_divide) & 1)) ? 0x10 : 0xd0;
+      src.push_back(color);
+      src.push_back(color);
+      src.push_back(color);
+      src.push_back(255);
+    }
+  }
+
+  std::vector<u8> dst(dst_sz * dst_sz * 4);
+  Timer timer;
+  resize_rgba_image(dst.data(), dst_sz, dst_sz, src.data(), src_w, src_h, true, true);
+  printf("resized in %.3f ms\n", timer.getMs());
+  file_util::write_rgba_png("test_wrap.png", dst.data(), dst_sz, dst_sz);
+  resize_rgba_image(dst.data(), dst_sz, dst_sz, src.data(), src_w, src_h, false, false);
+  printf("resized in %.3f ms\n", timer.getMs());
+  file_util::write_rgba_png("test_unwrap.png", dst.data(), dst_sz, dst_sz);
+  file_util::write_rgba_png("src.png", src.data(), src_w, src_h);
+
+  return 0;
+}