Support splatting `...` in egraphs pattern matching

[0x0f0f0f]

Support splatting in left and right hand of rules in the e-graph e-matcher. Example:

t = @theory begin 
    f(args...) => foo(args[1:2]...) + bar(args[2:end]...)
end

This is already supported by the MatchCore backend.

Splatting in left hand of rules requires modifying the pattern matcher. Splatting in right hand of rules does in fact require supporting dynamic rewrites.