Make browser APIs internal (#290)

These probably make sense to be public, but let's do that after they've been reviewed.

Author: twsouthwick

src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/IBrowserCapabilitiesFactory.cs

@@ -4,7 +4,7 @@
 namespace Microsoft.AspNetCore.SystemWebAdapters;
 
 #if NET6_0_OR_GREATER
-public interface IBrowserCapabilitiesFactory
+internal interface IBrowserCapabilitiesFactory
 {
     IHttpBrowserCapabilityFeature Create(HttpRequestCore request);
 }

src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/IHttpBrowserCapabilityFeature.cs

@@ -4,7 +4,7 @@
 namespace Microsoft.AspNetCore.SystemWebAdapters;
 
 #if NET6_0_OR_GREATER
-public interface IHttpBrowserCapabilityFeature
+internal interface IHttpBrowserCapabilityFeature
 {
     string? this[string key] { get; }
 }