Update documentation for new confirmation() overload. (#784)

Follow-up to #691. Updates DocC links now that `confirmation()` is
overloaded, specifies a minimum Swift version needed to use it, and adds
content to "Migrating From XCTest" covering the new overload.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/Issues/Confirmation.swift

@@ -160,7 +160,7 @@ public func confirmation<R>(
 /// preconditions have been met, and records an issue if they have not.
 ///
 /// If an exact count is expected, use
-/// ``confirmation(_:expectedCount:isolation:sourceLocation:_:)`` instead.
+/// ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-5mqz2`` instead.
 public func confirmation<R>(
   _ comment: Comment? = nil,
   expectedCount: some RangeExpression<Int> & Sequence<Int> & Sendable,
@@ -183,7 +183,7 @@ public func confirmation<R>(
   return try await body(confirmation)
 }
 
-/// An overload of ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-6bkl6``
+/// An overload of ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-l3il``
 /// that handles the unbounded range operator (`...`).
 ///
 /// This overload is necessary because `UnboundedRange` does not conform to
@@ -200,7 +200,7 @@ public func confirmation<R>(
   fatalError("Unsupported")
 }
 
-/// An overload of ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-6bkl6``
+/// An overload of ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-l3il``
 /// that handles the partial-range-through operator (`...n`).
 ///
 /// This overload is necessary because the lower bound of `PartialRangeThrough`
@@ -216,7 +216,7 @@ public func confirmation<R>(
   fatalError("Unsupported")
 }
 
-/// An overload of ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-6bkl6``
+/// An overload of ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-l3il``
 /// that handles the partial-range-up-to operator (`..<n`).
 ///
 /// This overload is necessary because the lower bound of `PartialRangeUpTo` is

Sources/Testing/Issues/Issue.swift

@@ -33,7 +33,7 @@ public struct Issue: Sendable {
     ///     ``Confirmation/confirm(count:)`` should have been called.
     ///
     /// This issue can occur when calling ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-5mqz2``
-    /// or ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-6bkl6``
+    /// or ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-l3il``
     /// when the confirmation passed to these functions' `body` closures is
     /// confirmed too few or too many times.
     indirect case confirmationMiscounted(actual: Int, expected: any RangeExpression & Sendable)
@@ -306,9 +306,9 @@ extension Issue.Kind {
     ///     ``Confirmation/confirm(count:)`` should have been called.
     ///
     /// This issue can occur when calling
-    /// ``confirmation(_:expectedCount:isolation:sourceLocation:_:)`` when the
-    /// confirmation passed to these functions' `body` closures is confirmed too
-    /// few or too many times.
+    /// ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-5mqz2`` when
+    /// the confirmation passed to these functions' `body` closures is confirmed
+    /// too few or too many times.
     indirect case confirmationMiscounted(actual: Int, expected: Int)
 
     /// An issue due to an `Error` being thrown by a test function and caught by

Sources/Testing/Testing.docc/AvailabilityStubs/Issues/Confirmation.md

@@ -0,0 +1,5 @@
+# ``Testing/confirmation(_:expectedCount:isolation:sourceLocation:_:)-l3il``
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}

Sources/Testing/Testing.docc/Expectations.md

@@ -76,7 +76,7 @@ the test when the code doesn't satisfy a requirement, use
 
 - <doc:testing-asynchronous-code>
 - ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-5mqz2``
-- ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-6bkl6``
+- ``confirmation(_:expectedCount:isolation:sourceLocation:_:)-l3il``
 - ``Confirmation``
 
 ### Retrieving information about checked expectations