Consider renaming `ConfigureHostApplicationBuilder` to `ConfigureWebApplicationBuilder`

Are we still planning to make this change? I like it. Even though the signature is `IHostApplicationBuilder` again, the object will always be a `WebApplicationBuilder`, not a `HostApplicationBuilder` (at least not directly). I also wonder if `ConfigureWebApplicationBuilder` might not be a better name for the public API since that's the only host type supported by that method. I wouldn't hold this PR on that though. I definitely want to get the already-approved API merged first. But if there's consensus that `ConfigureWebApplicationBuilder` is better (despite still taking an `IHostApplcationBuilder` argument), we can do that as a fast follow. _Originally posted by @halter73 in https://github.com/dotnet/aspnetcore/pull/66527#discussion_r3462104742_