Allow adjusting the recursion limit and stop masking overflows

This is particularly important for deeply nested types, which generate deeply nested impls. This is a fix for #19318. It's possible we could also improve this particular case not to increment the recursion count, but it's worth being able to adjust the recursion limit anyhow.

cc @jdm 
r? @pcwalton 
You can shrink this tower a bit with `if let`.