[Blazor] Disable problematic runtime switches, same as preview5 (#41412)

* Enables NullabilityInfoContextSupport from webassembly projects.
* Disables _AggressiveAttributeTrimming from webassembly projects.

There is a 0.76% size regression with these changes that unfortunately we need to take. Same was done in preview5.

src/BlazorWasmSdk/Targets/Microsoft.NET.Sdk.BlazorWebAssembly.6_0.targets

@@ -46,8 +46,6 @@ Copyright (c) .NET Foundation. All rights reserved.
     <UseSystemResourceKeys Condition="'$(UseSystemResourceKeys)' == ''">true</UseSystemResourceKeys>
     <EnableUnsafeUTF7Encoding Condition="'$(EnableUnsafeUTF7Encoding)' == ''">false</EnableUnsafeUTF7Encoding>
     <HttpActivityPropagationSupport Condition="'$(HttpActivityPropagationSupport)' == ''">false</HttpActivityPropagationSupport>
-    <NullabilityInfoContextSupport Condition="'$(NullabilityInfoContextSupport)' == ''">false</NullabilityInfoContextSupport>
-    <_AggressiveAttributeTrimming Condition="'$(_AggressiveAttributeTrimming)' == ''">true</_AggressiveAttributeTrimming>
     <DebuggerSupport Condition="'$(DebuggerSupport)' == '' and '$(Configuration)' != 'Debug'">false</DebuggerSupport>
     <BlazorCacheBootResources Condition="'$(BlazorCacheBootResources)' == ''">true</BlazorCacheBootResources>