[ast] Add BlockStatement

This CL adds a BlockStatement to wrap the statements in a given block.

Bug: tint:130
Change-Id: Idc2389e001d9d87ef7f45dcd8aa90bbd27ff7dce
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25606
Reviewed-by: Sarah Mashayekhi <sarahmashay@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 035e61f..24a19b0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -229,6 +229,8 @@
     "src/ast/binary_expression.h",
     "src/ast/binding_decoration.cc",
     "src/ast/binding_decoration.h",
+    "src/ast/block_statement.cc",
+    "src/ast/block_statement.h",
     "src/ast/bool_literal.cc",
     "src/ast/bool_literal.h",
     "src/ast/break_statement.cc",
@@ -667,6 +669,7 @@
     "src/ast/assignment_statement_test.cc",
     "src/ast/binary_expression_test.cc",
     "src/ast/binding_decoration_test.cc",
+    "src/ast/block_statement_test.cc",
     "src/ast/bool_literal_test.cc",
     "src/ast/break_statement_test.cc",
     "src/ast/builtin_decoration_test.cc",