Fix oss-fuzz build failure

A warning of a uint64_t -> size_t is causing the build to fail on 32-bit builds

Bug: oss-fuzz:45451
Change-Id: Iffaf2818d187b0659c10bd75229bb7c03f4f69df
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/83841
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/tint/sem/bool_type.cc

@@ -28,7 +28,7 @@ Bool::Bool(Bool&&) = default;
 Bool::~Bool() = default;
 
 size_t Bool::Hash() const {
-  return TypeInfo::Of<Bool>().full_hashcode;
+  return static_cast<size_t>(TypeInfo::Of<Bool>().full_hashcode);
 }
 
 bool Bool::Equals(const Type& other) const {

src/tint/sem/external_texture_type.cc

@@ -28,7 +28,7 @@ ExternalTexture::ExternalTexture(ExternalTexture&&) = default;
 ExternalTexture::~ExternalTexture() = default;
 
 size_t ExternalTexture::Hash() const {
-  return TypeInfo::Of<ExternalTexture>().full_hashcode;
+  return static_cast<size_t>(TypeInfo::Of<ExternalTexture>().full_hashcode);
 }
 
 bool ExternalTexture::Equals(const sem::Type& other) const {

src/tint/sem/f32_type.cc

@@ -28,7 +28,7 @@ F32::F32(F32&&) = default;
 F32::~F32() = default;
 
 size_t F32::Hash() const {
-  return TypeInfo::Of<F32>().full_hashcode;
+  return static_cast<size_t>(TypeInfo::Of<F32>().full_hashcode);
 }
 
 bool F32::Equals(const Type& other) const {

src/tint/sem/i32_type.cc

@@ -28,7 +28,7 @@ I32::I32(I32&&) = default;
 I32::~I32() = default;
 
 size_t I32::Hash() const {
-  return TypeInfo::Of<I32>().full_hashcode;
+  return static_cast<size_t>(TypeInfo::Of<I32>().full_hashcode);
 }
 
 bool I32::Equals(const Type& other) const {

src/tint/sem/u32_type.cc

@@ -28,7 +28,7 @@ U32::~U32() = default;
 U32::U32(U32&&) = default;
 
 size_t U32::Hash() const {
-  return TypeInfo::Of<U32>().full_hashcode;
+  return static_cast<size_t>(TypeInfo::Of<U32>().full_hashcode);
 }
 
 bool U32::Equals(const Type& other) const {

src/tint/sem/void_type.cc

@@ -28,7 +28,7 @@ Void::Void(Void&&) = default;
 Void::~Void() = default;
 
 size_t Void::Hash() const {
-  return TypeInfo::Of<Void>().full_hashcode;
+  return static_cast<size_t>(TypeInfo::Of<Void>().full_hashcode);
 }
 
 bool Void::Equals(const Type& other) const {