Dead-end blocks are blocks from which there is no path to the function exit (`return`, `throw` or unwind).
These are blocks which end with an unreachable instruction and blocks from which all paths end in "unreachable" blocks.
Replace the `struct EscapeInfo` with a simpler API, just consisting of methods of `ProjectedValue` and `Value`:
* `isEscaping()`
* `isAddressEscaping()`
* `visit()`
* `visitAddress()`
A projected value consists of the original value and a projection path.
For example, if the `value` is of type `struct S { var x: Int }` and `path` is `s0`, then the projected value represents field `x` of the original value.
Also, use ProjectedValue instead of AccessStoragePath.
