Add a way for code generators to replace a file.

[orellabac]

Currently the Context only has methods to add a new compilation unit but in my case I want a generator that will completely replace the contents of the original file. How can I do that?

[carldebilly]

Current the best way to achieve that is to use partial classes and/or create code which are only used by the generator, not the compiled app.

For now, it can only add new code and there's many ways to use that even with such limitation.