Expose [xctoolchain] subtarget for [dwarf-and-dsym]

Summary: To debug iOS tests, fdb needs the `[xctoolchain]` subtarget to materialize the correct version of `lldb-dap`. Because tests need to be built with `[dwarf-and-dsym]` to contain debugging information, this diff adds the `[xctoolchain]` subtarget as a subtarget of `[dwarf-and-dsym]`.

Reviewed By: patskovn

Differential Revision: D64036919

fbshipit-source-id: cc6d4c4a50ae20736e32391ff3281b53621885ea

apple/apple_test.bzl

@@ -191,7 +191,7 @@ def apple_test_impl(ctx: AnalysisContext) -> [list[Provider], Promise]:
         sub_targets["ui-test-target"] = [DefaultInfo(default_output = ui_test_target_app_bundle)] if ui_test_target_app_bundle else [DefaultInfo()]
 
         sub_targets[DWARF_AND_DSYM_SUBTARGET] = [
-            DefaultInfo(default_output = xctest_bundle, other_outputs = [dsym_artifact]),
+            DefaultInfo(default_output = xctest_bundle, other_outputs = [dsym_artifact], sub_targets = {_XCTOOLCHAIN_SUB_TARGET: ctx.attrs._apple_xctoolchain.providers}),
             _get_test_info(ctx, xctest_bundle, test_host_app_bundle, dsym_artifact, ui_test_target_app_bundle),
         ]