stdlib helpers: literal, layernorm, unsqueeze

[statusfailed]

Add some helpers:

• Literal: add a helper to create F32 / U32 literals and use in the GPT2 implementation
• LayerNorm
  • Move LayerNorm to stdlib, reduce boilerplate using helpers
  • Create a Module for LayerNorm operating on rank-2 tensors, and a helper to call it
• Squeeze / Unsqueeze helpers