Reland "[ DDS ] Fix DDS AOT snapshot build rules"

This is a reland of commit 0a393f1b69

The problem was that the checks for whether or not dartaotruntime
existed were always returning false on Windows because the ".exe" suffix
wasn't being taken into account. Patchset 2 addresses this.

Original change's description:
> [ DDS ] Fix DDS AOT snapshot build rules
>
> dds_aot.dart.snapshot was not being generated for runtime build targets,
> and dds.dart.snapshot was being built regardless of whether or not we
> were building for an IA32 target.
>
> This change also adds a check for IA32 in 'dart run' so the "Could not
> find dds_aot.dart.snapshot. Have you built the full Dart SDK?" message
> isn't printed when we fall back to using dds.dart.snapshot.
>
> This change also reverts 2cc08595a6, which
> failed to fix the issue it was attempting to fix.
>
> TEST=pkg/vm_service tests
>
> Change-Id: Ic990082c25b0d022093ad66600332dfb2878709f
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/341760
> Reviewed-by: Siva Annamalai <asiva@google.com>
> Commit-Queue: Ben Konyi <bkonyi@google.com>

TEST=pkg-win-release-try, pkg-win-release-arm64-try, and pkg/vm_service
tests

Change-Id: Ieab41edcb6bffca3be6bf628e357871f28949323
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/342640
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Derek Xu <derekx@google.com>

utils/dartdev/BUILD.gn

@@ -22,7 +22,14 @@ copy("copy_dartdev_snapshot") {
 application_snapshot("generate_dartdev_snapshot") {
   main_dart = "../../pkg/dartdev/bin/dartdev.dart"
   training_args = [ "--help" ]
+
   deps = [ "../dds:dds" ]
+
+  # DDS should be run from AOT snapshot on all architectures except IA32/X86.
+  if (dart_target_arch != "ia32" && dart_target_arch != "x86") {
+    deps += [ "../dds:dds_aot" ]
+  }
+
   vm_args = [ "--sound-null-safety" ]
   output = "$root_gen_dir/dartdev.dart.snapshot"
 }