Tpetra: Deprecate and remove DefaultPlatform, MpiPlatform, and SerialPlatform

Created by: mhoemmen

@trilinos/tpetra

Expectations

Tpetra should have a single source for initialization and for default values of template parameters.

Motivation and Context

Tpetra::DefaultPlatform is a hold-over from an old Tpetra initialization model that included something called HybridPlatform. Tpetra now has different plans for truly hybrid (e.g., GPU + CPU concurrently) parallelism, that the "platform" concept would not support. Furthermore, Platform is tied to Node, but we want to get rid of Node (#57).

Definition of Done

• Replace all use of Tpetra::DefaultPlatform to initialize Tpetra with Tpetra::ScopeGuard
• Replace all use of Tpetra::DefaultPlatform::DefaultPlatformType::NodeType with Tpetra::Map<>::node_type
• Deprecate Tpetra::DefaultPlatform, Tpetra::MpiPlatform, and Tpetra::SerialPlatform
• Remove Tpetra::DefaultPlatform, Tpetra::MpiPlatform, and Tpetra::SerialPlatform

Related Issues

• Blocked by #3119 (closed)
• Blocks #57