Create a catch-all grammar node for capturing anything of the format {{*}} to enable a generalized invalid / incorrect feelers validation

[Skaiir]

Is your feature request related to a problem? Please describe.

We currently have incomplete linting; a user may write invalid templates but be unaware of why they are invalid.

Describe the solution you'd like

I think treating anything of the format {{*}} as feelers syntax using some kind of low priority catch-all in the grammar, and then trying to parse it with more specific selectors would let us apply linting rules to anything that doesn't match the specific ones.

I think this would be useful to catch syntax like {{#for array}} which is just invalid.

Describe alternatives you've considered

We could leave the linting as-is, which already has some generic syntax error handling, but it won't give us the level of control we would want, especially when it comes to feelers-specific syntax.