Revert Enforce WebSockets Transport for Blazor

[TanayParikh]

Based on user feedback on the blog post / internal / github, we're re-considering the breaking change which disabled long polling as a fallback transport for SignalR in Blazor Server.

Description

Reverting changes introduced in #34644, which enforced WebSockets as the only available transport. Long polling was disabled as a fallback transport, due to concerns about user experience.

Customer Impact

This was a breaking change (announcement / docs). However, based on the feedback received in the recent RC1 release, more users are still utilizing long polling than expected.