Apply all changes from Configura to the public MPS.

[gareth-rees]

These changes were originally implemented as custom work for Configura on the custom/cet/main branch. With permission from the customer (see e-mail from Göran Rydqvist) we apply them to the public MPS, and integrate the custom documentation and interfaces into the public manual and headers.

The custom interfaces are as follows:

1. The Transforms interface provides a mechanism to rewrite references throughout the MPS-managed heap;

2. The Arena extension/contraction callbacks provide a mechanism for the client to register stack decoding callbacks on Windows managed runtime;

3. The hash arrays flag for allocation points prevents the MPS from aggressively collecting address-based hash tables.