* "merge" the `Path` and `State` in WalkUtils into a single `WalkingPath`. This makes it simpler for clients to configure a path and additional state variables. EscapeInfo now defines `EscapePath` which includes the projection path and EscapeInfo's specific state variables.
* Make the `WalkerCache` part of the WalkUtils, so that not all clients have to re-implement it.
* Rename `walkDownResults` -> `walkDownAllResults` and `walkUpOperands` -> `walkUpAllOperands` and make these functions client configurable.
`EscapeInfo` now conforms to the generic protocols defined in `WalkUtils`.
This simplifies the implementation a bit, since trivial instructions are handled
by `WalkUtils` and `EscapeInfo` only has to handle a subset of instructions
inherent to escape information.
Passes using `EscapeInfo` are updated accordingly to become visitors that
customize the `EscapeInfo` walk.
