This PR creates the initial scaffolding for the codegen preprocessor.
The preprocessor is a target-specific binary that will take a model,
load it into a TFLM Interpreter, perform the Init & Prepare stages, then
serialize the resulting data structures to an output file. Currently,
all this binary does is load the model file and write an output file
that simply contains the source model path in it. This will be expanded
as we expose the data.

BUG=b/295076056

The codegen process is a multi-step process that requires compiling,
executing code under simulation, and executing python scripts. To
simplify this workflow, this commit adds Make helper functions for
generating inference source code from a model and creating a binary with
it.

It also updates the hello world example to use these helpers and adds an
update script for keeping the checked in generated source in sync.