Avoid creating identity to obtain public key (#78255)

Reduce allocations in AssemblySymbol.GivesAccessTo due to getting the assemblyWantingAccess's Identity.

During the completion scenarios in the C# speedometer tests, about 3% of allocations in the VS process are used obtaining this identity just to get the PublicKey. However, in the case where assemblyWantingAccess is an AssemblySymbol, there is a way to obtain this without needing to obtain the full Identity.

See PR for images outlining before / after allocation patterns.

Author: ToddGrun

src/Compilers/CSharp/Portable/Symbols/PublicModel/AssemblySymbol.cs

@@ -81,9 +81,15 @@ bool IAssemblySymbol.GivesAccessTo(IAssemblySymbol assemblyWantingAccess)
 
                 AssemblyIdentity identity = UnderlyingAssemblySymbol.Identity;
 
+                // Avoid using the identity to obtain the public key if possible to avoid the allocations associated
+                // with identity creation
+                ImmutableArray<byte> publicKey = (assemblyWantingAccess is AssemblySymbol assemblyWantingAccessAssemblySymbol)
+                    ? assemblyWantingAccessAssemblySymbol.UnderlyingAssemblySymbol.PublicKey.NullToEmpty()
+                    : assemblyWantingAccess.Identity.PublicKey;
+
                 foreach (var key in myKeys)
                 {
-                    IVTConclusion conclusion = identity.PerformIVTCheck(assemblyWantingAccess.Identity.PublicKey, key);
+                    IVTConclusion conclusion = identity.PerformIVTCheck(publicKey, key);
                     Debug.Assert(conclusion != IVTConclusion.NoRelationshipClaimed);
                     if (conclusion == IVTConclusion.Match || conclusion == IVTConclusion.OneSignedOneNot)
                     {

src/Compilers/VisualBasic/Portable/Symbols/AssemblySymbol.vb

@@ -750,8 +750,13 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
                 Return True
             End If
 
+            ' Avoid using the identity to obtain the public key if possible to avoid the allocations associated
+            ' with identity creation
+            Dim assemblyWantingAccessAssemblySymbol As AssemblySymbol = TryCast(assemblyWantingAccess, AssemblySymbol)
+            Dim publicKey = If(assemblyWantingAccessAssemblySymbol IsNot Nothing, assemblyWantingAccessAssemblySymbol.PublicKey.NullToEmpty(), assemblyWantingAccess.Identity.PublicKey)
+
             For Each key In myKeys
-                Dim conclusion As IVTConclusion = Me.Identity.PerformIVTCheck(assemblyWantingAccess.Identity.PublicKey, key)
+                Dim conclusion As IVTConclusion = Me.Identity.PerformIVTCheck(publicKey, key)
                 Debug.Assert(conclusion <> IVTConclusion.NoRelationshipClaimed)
                 If conclusion = IVTConclusion.Match Then
                     ' Note that C# includes  OrElse conclusion = IVTConclusion.OneSignedOneNot