[WebGPU] ThreeJS video samples fail MSL compilation

https://bugs.webkit.org/show_bug.cgi?id=268593
<radar://122146692>

Reviewed by Tadeu Zagallo.

ExternalTextures should have Handle AccessMode, not Uniform.

* Source/WebGPU/WGSL/GlobalVariableRewriter.cpp:
(WGSL::addressSpaceForBindingMember):

Canonical link: https://commits.webkit.org/273981@main

Source/WebGPU/WGSL/GlobalVariableRewriter.cpp

@@ -1251,7 +1251,7 @@ static AddressSpace addressSpaceForBindingMember(const BindGroupLayoutEntry::Bin
     }, [](const StorageTextureBindingLayout&) {
         return AddressSpace::Handle;
     }, [](const ExternalTextureBindingLayout&) {
-        return AddressSpace::Uniform;
+        return AddressSpace::Handle;
     });
 }