Perf: Investigate optimizations around AcquireTokenSilentSupplier.getAuthorityWithPrefNetworkHost

[billwert]

While doing some perf investigations on Azure Identity I noticed that we spend a ton of time in getAuthorityWithPrefNetworkHost when getting tokens out of the cache. The perf test is literally calling acquireTokenForManagedIdentity in a hot loop with no parameters or authority configured.

It ends up being ~70% of the time under AcquireSilentTokenSupplier.execute():

Discussion with @Avery-Dunn offline leads to the thought that we can optimize this path some - there's no reason to recompute and reconstruct an authority every call.

This should be investigated in the silent, device code, and auth grant flows.