[dart2wasm] New async* desugaring

See `_lowerAsyncStar` for the desugaring plan.

Fixes tests:

co19/Language/Expressions/Function_Invocation/async_generator_invokation_t04
co19/Language/Expressions/Function_Invocation/async_generator_invokation_t08
co19/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_A01_t07
co19/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_A03_t04
co19/Language/Statements/Yield_and_Yield_Each/Yield/execution_async_A03_t05
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t03
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t07
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t08
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t09
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t11
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t12
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t14
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t15
co19/Language/Statements/Yield_and_Yield_Each/Yield_Each/execution_async_A03_t16
language/async_star/async_star_await_for_test
language/async_star/async_star_cancel_test
language/async_star/async_star_test
language/async_star/throw_in_catch_test
language/async_star/yield_test
language/async_star/yieldstar_test
lib/async/async_await_zones_test

Fixes #55025.
Fixes #55018.
Fixes #52464.

Change-Id: I9d51564698710993cb7d2cc64b3bb8c26d6d4c77
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/355360
Commit-Queue: Ömer Ağacan <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>

Author: osa1