Adds support for 'Context' parameters on components
This change allows you to set the parameter name of a parameterized child content by using the `Context` attribute on the component. The `Context` attribute will be defined (and shown by completion) when the component has one or more declared parameterized (`RenderFragment<>`) child content parameters.
This is nice for cases where you are using implicit child content:
```
<ol>
<Repeater Items="People" Context="person">
<li>@person.FirstName</li>
</Repeater>
</ol>
```
or, when you have multiple child content elements and want them all to have the same parameter name:
```
<MyComponent Items="People" Context="person">
<ChildContent1><div>@person.FirstName</div></ChildContent1>
<ChildContent2><div>@person.LastName</div></ChildContent2>
</Repeater>
```
The parameter name can be overridden by using the `Context` parameter on the child content element:
```
<MyComponent Items="People" Context="person">
<ChildContent1 Context="item"><div>@item.FirstName</div></ChildContent1>
<ChildContent2><div>@person.LastName</div></ChildContent2>
</Repeater>
```
If the component defines a `Context` parameter already then we won't synthesize one - your component's parameter will work exactly as it did before this feature.
* Test namespace cleanup
* Add recognication for RenderFragment in tag helpers
* Remove dead code from node writers
* refactor type check
* Continue to treat child content as a delegate in codegen
* Add extension to enumerate child content
* Reorganize code generation tests
These were growing a bit disorganized, and weren't really result in good
code reuse.
* fix test base class
* Add some child-content tests
* Add an explicit node for ChildContent
Adds a strongly typed node to represent a 'ChildContent' and what it
contains. This allows us to simplify the code generation path,
detect/processes more issues in IR passes, and will be essential for
supporting multiple child content.
* Ignore ChildContent in components when it's just whitespace
* Add diagnostic for duplicate child content
* Add support for explicit child content elements
Precursor to support for multiple child content items
* Add support for multiple child-content elements
* Change delegate signature for RenderFragment<T>
* Clean up Tag Helper constants
* Allow RenderFragment<T> as a child content
* Allow renaming the template parameter
* Improve error message for invalid child content
* Add diagnostic for repeated child content parameter names
Ryan Nowak