Fix: Top-level symbols are now all verified. (#4443)

Fixes #4442
In #4427, a bug was introduced
which prevent multiple top-level verification symbols to be reported,
only the first one would. This adds a test to cover the issue and fixes
it. I verified that the test was failing before the fix, and now the
test is passing. I am not adding a docs/dev/news entry because the bug
was introduced after the 4.2.0 release.

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license](https://github.com/dafny-lang/dafny/blob/master/LICENSE.txt).</small>

Source/DafnyCore/Generic/NodeExtensions.cs

@@ -115,18 +115,11 @@ public static IEnumerable<LList<INode>> FindNodeChainsInUri(this INode node, Uri
  return new[] { new LList<INode>(node, parent) };
  }
 
- return null;
+ return new LList<INode>[] { };
  }
 
  var newParent = new LList<INode>(node, parent);
- foreach (var child in node.Children) {
- var result = child.FindNodeChainsInUri(uri, newParent);
- if (result != null) {
- return result;
- }
- }
-
- return null;
+ return node.Children.SelectMany(child => child.FindNodeChainsInUri(uri, newParent));
  }
 
  private static LList<INode> FindNodeChain(this INode node, Uri uri, DafnyPosition position, LList<INode> parent,

Source/DafnyLanguageServer.Test/Lookup/DocumentSymbolTest.cs

@@ -46,6 +46,22 @@ method DoIt() returns (x: int) {
  Assert.Single(cChildren);
  }
 
+ [Fact]
+ public async Task LoadCorrectDocumentCreatesTopLevelSymbols() {
+ var source = @"
+ method DoIt() returns (x: int) {
+ }
+
+ method CallIt() returns () {
+ var x := DoIt();
+ }".TrimStart();
+ var documentItem = CreateTestDocument(source);
+ await client.OpenDocumentAndWaitAsync(documentItem, CancellationToken);
+ var allSymbols = await RequestDocumentSymbol(documentItem);
+ Assert.Equal(2, allSymbols.Count());
+ }
+
+
  [Fact]
  public async Task LoadCorrectDocumentCreatesSymbols() {
  var source = @"