Replace Literal::(Is|As)* with Castable

Change-Id: I842483890b369d63c23dba475b6738bffe5cfdbd
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/34319
Reviewed-by: dan sinclair <dsinclair@chromium.org>
diff --git a/src/reader/wgsl/parser_impl_inclusive_or_expression_test.cc b/src/reader/wgsl/parser_impl_inclusive_or_expression_test.cc
index 207fcd9..12b1ddb 100644
--- a/src/reader/wgsl/parser_impl_inclusive_or_expression_test.cc
+++ b/src/reader/wgsl/parser_impl_inclusive_or_expression_test.cc
@@ -44,8 +44,8 @@
   ASSERT_TRUE(rel->rhs()->Is<ast::ConstructorExpression>());
   ASSERT_TRUE(rel->rhs()->Is<ast::ScalarConstructorExpression>());
   auto* init = rel->rhs()->As<ast::ScalarConstructorExpression>();
-  ASSERT_TRUE(init->literal()->IsBool());
-  ASSERT_TRUE(init->literal()->AsBool()->IsTrue());
+  ASSERT_TRUE(init->literal()->Is<ast::BoolLiteral>());
+  ASSERT_TRUE(init->literal()->As<ast::BoolLiteral>()->IsTrue());
 }
 
 TEST_F(ParserImplTest, InclusiveOrExpression_InvalidLHS) {