Use modern hash factories for SHA CSP locals used once

Replace a parameterless SHA1/SHA256/SHA384/SHA512CryptoServiceProvider local used once by an immediately following ComputeHash return, initializer, plain local assignment or discarded call with the same algorithm's modern Create() factory. Modern .NET wraps the same hash provider. Preserve argument evaluation and the ComputeHash overload. Leave escaping/reused providers, CNG classes, settings, disposal scopes, fallback factories, async/iterator blocks and conditional snapshots unchanged. Opt-in; no algorithm upgrade.