This allows users of Visual Studio Code to open the sdk/ directory.
Without this, attempting to open the root of the repository results
in over 200k analyzer errors eventually hanging/crashing VSCode.
This matches what Fuschia and other large projects do to be able
to open large monorepo checkouts in VSCode. e.g.
https://fuchsia.googlesource.com/fuchsia/+/main/fuchsia.code-workspace
Bug: https://github.com/dart-lang/sdk/issues/52380
Change-Id: I1a69627bb6ca25e8f7f036a50534eaf0804e893e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/303841
Reviewed-by: Devon Carew <devoncarew@google.com>
Commit-Queue: Devon Carew <devoncarew@google.com>
Auto-Submit: Eric Seidel <eric@shorebird.dev>
