Refactored CodeGeneratorContext to CodeBuilderContext.

- Needed to separate the context's of "generation" and "building" to enable the communication of the TagHelperProvider.
There's already a context that the parser uses and initializes in its parse method (dependent on its own member values).  
Options:
1. Add an ```out``` parameter to the parse method that "provides" the ```TagHelperProvider```.
2. Add callback for ```TagHelperProvider``` (pretty much just like an ```out``` param but not an ```out``` param lol).
3. Pass in a ```TagHelperProvider``` builder of some sort into the ```RazorParser```'s ctor and use it to create the TagHelperProvider when parse is called.  We can then pull from the builder.
4. Expose the ```TagHelperProvider``` on the ```RazorParser``` itself.
5. Leave it on ```ParserResults```.
6. As a part of #112 and #111 a tag helper locator can be passed into the ctor which can then be utilized to  fetch the ```TagHelperProvider``` off of.  As a temporary fix for this PR until those issues are completed I can provide a dummy implementation of it.