Effects: keep track of CPS calls and distinguish CPS calls and trampolined calls

[OlivierNicole]

This makes a more precise distinction between CPS calls and trampolined calls, and keeps track of both. It is used in wasm_of_ocaml to handle CPS calls.

This PR is the first in a series of PRs intending to reduce the diff between js_of_ocaml and wasm_of_ocaml, in order to merge the two repos eventually, or at least to ease integration of JSOO updates in WSOO.

[vouillon]

CPS calls are calls that take a continuation as the last parameter. We also have direct calls which may make use of the trampoline: they are used to implement loops. In the current implementation, we don't really distinguish them since these direct calls are exact, and the JS implementation behaves the same for direct calls whether in CPS or not (just apply the function to all its arguments).
This is no longer true with wasm_of_ocaml where the two kind of functions have different types.
We also need to make the distinction for the double translation (#1461).