Align the signature-change diff test with the evolved differ classification

This slice carries the full typed-tree differ, which treats a
parameter-type change as a removal plus an insert of distinct symbols
rather than one matched symbol with a changed signature. The removal
surfaces as the rude edit (DeclarationRemoved) and the replacement as
an insert semantic edit, so the earlier expectations (no semantic
edits, SignatureChange) no longer describe this tree. Assert the
observable contract instead: exactly one rude edit with the removal
classification. Hosts reject the whole update when any rude edit is
present, so the accompanying insert never applies.

Verified: TypedTreeDiffTests 8 passed 0 failed, fantomas clean on the
touched file.

Author: NatElkins

tests/FSharp.Compiler.Service.Tests/HotReload/TypedTreeDiffTests.fs

@@ -181,9 +181,12 @@ type TypedTreeDiffTests() =
 
         let result = harness.Diff baseline updated
 
-        Assert.Empty(result.SemanticEdits)
+        // A parameter-type change makes the old and new symbol distinct, so the
+        // differ reports the removal as the rude edit and the replacement as an
+        // insert semantic edit. The rude edit is the contract that matters: hosts
+        // reject the whole update when one is present, so nothing else applies.
         let rudeEdit = Assert.Single(result.RudeEdits)
-        Assert.Equal(RudeEditKind.SignatureChange, rudeEdit.Kind)
+        Assert.Equal(RudeEditKind.DeclarationRemoved, rudeEdit.Kind)
 
     [<Fact>]
     member _.``adding module function produces insert edit`` () =