Rename the IntLiteral to SintLiteral.

This Cl clarifies that IntLiteral is a signed value, which matches with
the usage of UintLiteral.

Change-Id: Ic8f0e2382cb66eb6b09daed096886dcc55e6b0f0
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/22540
Reviewed-by: David Neto <dneto@google.com>
diff --git a/src/ast/null_literal_test.cc b/src/ast/null_literal_test.cc
index 67354f6..62bd62e 100644
--- a/src/ast/null_literal_test.cc
+++ b/src/ast/null_literal_test.cc
@@ -27,7 +27,7 @@
   ast::type::I32Type i32;
   NullLiteral i{&i32};
   EXPECT_FALSE(i.IsBool());
-  EXPECT_FALSE(i.IsInt());
+  EXPECT_FALSE(i.IsSint());
   EXPECT_FALSE(i.IsFloat());
   EXPECT_FALSE(i.IsUint());
   EXPECT_TRUE(i.IsNull());
@@ -48,4 +48,4 @@
 
 }  // namespace
 }  // namespace ast
-}  // namespace tint
\ No newline at end of file
+}  // namespace tint