DSDLCodeGenerator filters are available to support templates

[thirtytwobits]

While nothing terrible comes of this it does rely on an unstable ordering of generator initialization. That is, when the support generator is initialized the DSDLCodeGenerator templates are not available, however, when generating code they are because the DSDLCodeGenerator added them to a shared environment when it initialized.

Possible fixes include:

1. just moving all the generator filters to the environment.
2. creating different environment objects per generator
3. sandboxing filters and tests based on the code generator in use (not recommended).