[vm] Ensure create_sdk GN build has working dart2native iff AOT is supported

This CL

   * adds a GN flag "include_dart2native" off by-default (switched on explicitly for our GN build)
   * ensures every GN build of the "create_sdk" target has a working dart2native (except ia32)
   * removes not-working dart2native script from ia32 dart-sdk (no AOT support in ia32)
   * removes the "dartaotruntime" GN target, since it is the same as "dart_precompiled_runtime"

This should ensure every downstream consumer of the "create_sdk" GN target will
have a working version of dart2native.

For the particular "dart-sdk" we create on dart-sdk-{linux,windows,mac}
we will override the default AOT compiler&runtime with the product mode,
which produces smaller AOT snapshots and has smaller AOT runtime (making
the native executables significantly smaller)

Change-Id: Ib5042589297cdb055c41dc56abdff86a4612ef5c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/123724
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Michael Thomsen <mit@google.com>