[dart2wasm] Refactor generate method into individual kinds
[dart2wasm] Refactor generate method into individual kinds

Change-Id: I6c41931232f6b3805271c85e544431763d2c747d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/241966
Reviewed-by: Joshua Litt <9f8daed1ab51574c9a48ffacb03e4a1adb4f880c@google.com>
Commit-Queue: Aske Simon Christensen <589eb3fd9a84f06d0ac46d3aa71dddcfb0814ccd@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk