When suggesting Patterns to Autocomplete, use Expr to influence generation

[StachuDotNet]

If I'm writing the code:

match Ok "testing"
  | ~___ -> ___

(with my cursor at the ~),

a limited standard set of Autocomplete Patterns are suggested. true, false, OK ___, etc.

Given that Dark has context of the Ok "testing" expression that we're matching against, it could be additionally useful to include `Ok "testing" as an option - the PString can be derived by the expr.

This is sort of contrived, but I suspect there are more cases where this sort of thing could be handy? Maybe not :)

[pbiggar]

I have been thinking to have a command that generates all possible cases for a particular type. Another way to do that would be like copilot: each line individually generated and accepted. In this case, we could just generate each possible sumtype from the type of the expression.