Build fails when thrift proxy extensions are disabled

[roelfdutoit]

The following build command fails:
bazel test //test/extensions/filters/network/...

.. when the following extensions are disabled in source/extensions/extensions_build_config.bzl:
envoy.filters.network.thrift_proxy
envoy.filters.thrift.router
envoy.filters.thrift.ratelimit

Build failure:

ERROR: test/extensions/filters/network/thrift_proxy/filters/BUILD:11:14: no such target '//test/extensions/filters/network/thrift_proxy:mocks': target 'mocks' not declared in package 'test/extensions/filters/network/thrift_proxy' defined by test/extensions/filters/network/thrift_proxy/BUILD and referenced by '//test/extensions/filters/network/thrift_proxy/filters:pass_through_filter_test'
ERROR: Analysis of target '//test/extensions/filters/network/thrift_proxy/filters:pass_through_filter_test' failed; build aborted: Analysis failed

I believe it is because the target in test/extensions/filters/network/thrift_proxy/filters/BUILD uses envoy_cc_test instead of envoy_extension_cc_test

[roelfdutoit]

The build command above succeeds with my local changes. I will submit a PR

[roelfdutoit]

@zuercher: This seems to be related to #12003.