fixup! docs: HashSet and ISet in the changelog and the collection table

Two sentences that the `SortedSet` branch found missing in the `HashSet` bullets, after it
verified that all eight mutating members of the BCL interfaces throw `NotSupportedException`
on `ImmutableHashSet`:

- The struct of `HashSet.forComparer` also replaces `ToImmutableHashSet(items, comparer)`.
- The mutating members of the BCL interfaces, such as `ISet<T>.UnionWith` and
  `ICollection<T>.Add`, throw `NotSupportedException` on a hash set and have no function.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Author: xperiandri

CHANGELOG.md

@@ -39,14 +39,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * `HashSet.forComparer comparer` creates the `CustomComparerHashSet` struct, whose members `build`, `builder`, `empty`,
   `ofArray`, `ofList`, `ofReadOnlySpan`, `ofSeq`, `ofSpan` and `singleton` create hash sets and builders that compare
   with the comparer, as in `(HashSet.forComparer StringComparer.OrdinalIgnoreCase).ofSeq names`. They replace the BCL
-  members `Create(comparer, ...)`, `CreateRange(comparer, items)` and `CreateBuilder(comparer)`. `ofSeq` also gives an
-  existing hash set the comparer, as `WithComparer` does: the hash set itself comes back for the same comparer
-  instance, and an equal but distinct instance rebuilds it. `WithComparer(null)` is `HashSet.ofSeq set`. A `null`
-  comparer throws `ArgumentNullException`.
+  members `Create(comparer, ...)`, `CreateRange(comparer, items)`, `ToImmutableHashSet(items, comparer)` and
+  `CreateBuilder(comparer)`. `ofSeq` also gives an existing hash set the comparer, as `WithComparer` does: the hash set
+  itself comes back for the same comparer instance, and an equal but distinct instance rebuilds it.
+  `WithComparer(null)` is `HashSet.ofSeq set`. A `null` comparer throws `ArgumentNullException`.
 * `HashSet.add` and `remove` return the input itself when nothing changes, so a reference comparison of the input and
   the result tells whether `Add` changed anything, as the `bool` result of `Builder.Add` does. Hash sets have no builder
   module: `builder`, `toBuilder` and `ofBuilder` are `CreateBuilder`, `ToBuilder` and `ToImmutable`, and the builder is
-  used directly.
+  used directly. The mutating members of the BCL interfaces, such as `ISet<T>.UnionWith` and `ICollection<T>.Add`,
+  throw `NotSupportedException` on a hash set and have no function.
 * `add`, `addRange`, `remove`, `removeRange`, `clear`, `update`, `filter` and `partition` of `HashSet` keep the comparer
   of their input, and the set algebra keeps the comparer of the first hash set; `map`, `choose` and `partitionWith`
   compare with the default comparer of the result type. Every function throws `ArgumentNullException` for a `null` hash