Add missing WGSL writer test files to BUILD.gn

These files were added in dfd1714, but only added to CMakeLists.txt.

Change-Id: I775e8fef68b2f4900a6c562533512f0eda01b795
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/41700
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index d2b2637..4d79363 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1116,8 +1116,10 @@
     "src/writer/wgsl/generator_impl_constructor_test.cc",
     "src/writer/wgsl/generator_impl_continue_test.cc",
     "src/writer/wgsl/generator_impl_discard_test.cc",
+    "src/writer/wgsl/generator_impl_entry_point_test.cc",
     "src/writer/wgsl/generator_impl_fallthrough_test.cc",
     "src/writer/wgsl/generator_impl_function_test.cc",
+    "src/writer/wgsl/generator_impl_global_decl_test.cc",
     "src/writer/wgsl/generator_impl_identifier_test.cc",
     "src/writer/wgsl/generator_impl_if_test.cc",
     "src/writer/wgsl/generator_impl_loop_test.cc",