[WIP] Proper grammar for concrete syntax

[danieltrt]

I hacked a grammar for concrete syntax from uber/tree-sitter-strings because:

1. Existing implementation of concrete syntax is hacked using string comparisons
2. Concrete syntax is limited in expressiveness compared to tree sitter query syntax because of 1.

The goal is to make concrete syntax more powerful. The version here supports:

:[x] and [x: node-type], which addresses the problem of being unable to use node types to further constraint the template variable types.

I was also thinking of addding a where syntax for basic operations like equality, and !=. Eventually it could be integrated with LSP for more powerful where queries