Add PublicAPI baselines for Identity (#25578)

Except Identity.UI, since it has Razor files.

Author: Pilchie

src/Identity/ApiAuthorization.IdentityServer/src/PublicAPI.Shipped.txt

@@ -0,0 +1 @@
+#nullable enable

src/Identity/ApiAuthorization.IdentityServer/src/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+#nullable enable

src/Identity/Core/src/PublicAPI.Shipped.txt

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Security.Claims;
 using System.Threading.Tasks;
@@ -197,6 +198,7 @@ public virtual async Task RefreshSignInAsync(TUser user)
         /// <param name="isPersistent">Flag indicating whether the sign-in cookie should persist after the browser is closed.</param>
         /// <param name="authenticationMethod">Name of the method used to authenticate the user.</param>
         /// <returns>The task object representing the asynchronous operation.</returns>
+        [SuppressMessage("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "Required for backwards compatibility")]
         public virtual Task SignInAsync(TUser user, bool isPersistent, string authenticationMethod = null)
             => SignInAsync(user, new AuthenticationProperties { IsPersistent = isPersistent }, authenticationMethod);
 
@@ -207,6 +209,7 @@ public virtual Task SignInAsync(TUser user, bool isPersistent, string authentica
         /// <param name="authenticationProperties">Properties applied to the login and authentication cookie.</param>
         /// <param name="authenticationMethod">Name of the method used to authenticate the user.</param>
         /// <returns>The task object representing the asynchronous operation.</returns>
+        [SuppressMessage("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "Required for backwards compatibility")]
         public virtual Task SignInAsync(TUser user, AuthenticationProperties authenticationProperties, string authenticationMethod = null)
         {
             IList<Claim> additionalClaims = Array.Empty<Claim>();

src/Identity/Core/src/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+#nullable enable

src/Identity/Core/src/SignInManager.cs

@@ -0,0 +1 @@
+#nullable enable