Fix API compat errors

Author: stephentoub

src/libraries/shims/ApiCompatBaseline.PreviousNetCoreApp.txt

@@ -23,4 +23,5 @@ CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Ru
 CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Runtime.Versioning.UnsupportedOSPlatformAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Constructor | AttributeTargets.Enum | AttributeTargets.Event | AttributeTargets.Field | AttributeTargets.Method | AttributeTargets.Module | AttributeTargets.Property | AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Constructor | AttributeTargets.Enum | AttributeTargets.Event | AttributeTargets.Field | AttributeTargets.Interface | AttributeTargets.Method | AttributeTargets.Module | AttributeTargets.Property | AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]' in the implementation.
 Compat issues with assembly System.Security.Cryptography.Algorithms:
 CannotRemoveAttribute : Attribute 'System.Runtime.Versioning.UnsupportedOSPlatformAttribute' exists on 'System.Security.Cryptography.CryptoConfig' in the contract but not the implementation.
-Total Issues: 15
+CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Runtime.CompilerServices.AsyncMethodBuilderAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Delegate | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Struct, Inherited=false, AllowMultiple=false)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Delegate | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Method | AttributeTargets.Struct, Inherited=false, AllowMultiple=false)]' in the implementation.
+Total Issues: 16

src/libraries/shims/ApiCompatBaseline.netcoreapp.netstandardOnly.txt

@@ -195,4 +195,5 @@ CannotRemoveAttribute : Attribute 'System.ComponentModel.BrowsableAttribute' exi
 CannotRemoveAttribute : Attribute 'System.ComponentModel.CategoryAttribute' exists on 'System.Timers.Timer.Elapsed' in the contract but not the implementation.
 CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Xml.Serialization.XmlAnyAttributeAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, AllowMultiple=false)]' in the implementation.
 CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Xml.Serialization.XmlNamespaceDeclarationsAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, AllowMultiple=false)]' in the implementation.
-Total Issues: 196
+CannotChangeAttribute : Attribute 'System.AttributeUsageAttribute' on 'System.Runtime.CompilerServices.AsyncMethodBuilderAttribute' changed from '[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Delegate | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Struct, Inherited=false, AllowMultiple=false)]' in the contract to '[AttributeUsageAttribute(AttributeTargets.Class | AttributeTargets.Delegate | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Method | AttributeTargets.Struct, Inherited=false, AllowMultiple=false)]' in the implementation.
+Total Issues: 198