Factored out most of the rr::Print code in LLVMReactor.cpp to
Reactor.cpp, and rewritten in terms of Nucleus. Added a couple of new
Nucleus functions to support this.

Bug: b/149477527
Change-Id: I0a28626f1aa6133a37f9e75abc08544f3de15a45
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/41188
Presubmit-Ready: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>