[ Service ] Include flags and options with custom handlers in getFlagList RPC response
[ Service ] Include flags and options with custom handlers in getFlagList
RPC response

Fixes https://github.com/dart-lang/sdk/issues/43588

Change-Id: I7fa98dd2218d182e80f682a2fd6a3a4150509dfb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/166260
Commit-Queue: Ben Konyi <67ffcaedcc3dc3d87dddb9627b72dd41756b31b1@google.com>
Reviewed-by: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@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