[hlsl-writer] Add support for import statements.

This Cl adds support for imported methods to the HLSL backend.

Bug: tint:7
Change-Id: Ib906542915670dcc916d48d9e5d64d7032ba829a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/26928
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: David Neto <dneto@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index e8648f8..423d670 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1073,6 +1073,7 @@
     "src/writer/hlsl/generator_impl_function_test.cc",
     "src/writer/hlsl/generator_impl_identifier_test.cc",
     "src/writer/hlsl/generator_impl_if_test.cc",
+    "src/writer/hlsl/generator_impl_import_test.cc",
     "src/writer/hlsl/generator_impl_intrinsic_test.cc",
     "src/writer/hlsl/generator_impl_loop_test.cc",
     "src/writer/hlsl/generator_impl_member_accessor_test.cc",