Rename mipLevel to levelCount in TextureDescriptor

This patch renames the field "mipLevel" of TextureDescriptor to
"levelCount" to align with the WebGPU idl.

BUG=dawn:16

Change-Id: I36b30d78831786e4c21ffd641f820375e95a1be5
Reviewed-on: https://dawn-review.googlesource.com/c/2100
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/examples/CppHelloTriangle.cpp b/examples/CppHelloTriangle.cpp
index c9aa88c..c1a8f50 100644
--- a/examples/CppHelloTriangle.cpp
+++ b/examples/CppHelloTriangle.cpp
@@ -55,7 +55,7 @@
     descriptor.size.depth = 1;
     descriptor.arrayLayer = 1;
     descriptor.format = dawn::TextureFormat::R8G8B8A8Unorm;
-    descriptor.mipLevel = 1;
+    descriptor.levelCount = 1;
     descriptor.usage = dawn::TextureUsageBit::TransferDst | dawn::TextureUsageBit::Sampled;
     texture = device.CreateTexture(&descriptor);