implement codegen of the new jsinterop in cpsir

[sigmundch]

No description provided.

[zoechi]

May I ask what "nssa" means? I saw it a few times recently but have no clue what it is about.

[sigmundch]

We have been doing some work to replace our ssa backend with the a cps-ir (continuation-passing-style IR), but we plan to do some refactoring changes that will remove the continuations from CPS-ir, which makes it more like a nested-ssa, or "nssa" for short :)

[zoechi]

Never mind :D
Thanks anyway!

[sigmundch]

I'll be sending https://codereview.chromium.org/1688433006 out shortly. The following two tests are still failing:

js_typed_interop_side_cast_exp_test: It's not clear whether we want to continue supporting these semantics of allowing a side-cast. I haven't investigated what makes this behave different than SSA, but it's quite possible this seems to be breaking some assumptions in type-propagation.

js_typed_interop_test/static_method_tearoff_1: this seems broken due to an unrelated issue with tree-shaking. It might be related to #25720.

The CL also adds js_typed_interop_test/static_method_tearoff_2: to illustrate issue #25759.

[sigmundch]

landed support in a0c438a. Closing since pending issues are tracked in the two bugs mentioned above.