Publish SyntaxRewriter.visitChildren

[beccadax]

There’s currently no good way to rewrite the children of a node while using SyntaxRewriter.visitAny(_:). This commit renames an existing internal method to visitChildren(of:) and makes it public so you can call it from a visitAny(_:) override.

This may not be the best way to address the issue; I'm open to alternatives. Or there might be some reason you're not supposed to do this at all, I suppose.

[harlanhaskins]

The issue with this is you force the creation of the new node, from a potentially unverified child layout, onto the client.

swift-format solves this by just keeping an instance variable of the currently visited node, and returning nil from visitAny if the provided node is that node.

[beccadax]

I could rework my code along those lines (actually, my visitAny(_:) is very similar to swift-format's, right down to the reduce), but if this is a common pattern, why is it so awkward to write?

I notice that both examples want to traverse depth-first, so one alternative might be to add a visitAnyPost(_:) or change visitPost(_:) to (optionally?) return a new value.