fix(bazel): add support for defining the platform used for bundling spec_bundle targets (#2870)

Previously the platform was hardcoded to node which worked by chance, but in some cases the platform should be
explicitly set to browser for web test which will run in a browser

PR Close #2870

Author: josephperrott

bazel/spec-bundling/index_rjs.bzl

@@ -31,7 +31,7 @@ def spec_bundle(name, deps, srcs = [], bootstrap = [], testonly = True, config =
         bundle = True,
         format = "iife",
         sourcemap = "linked",
-        platform = "node",
+        platform = kwargs.pop("platform", "node"),
         entry_point = ":%s_entrypoint" % name,
         output = "%s.spec.js" % name,
         **kwargs