Extract the instruction sequence data structure into its own file and add a Python interface

[iritkatriel]

The Instruction Sequence data structure used by the compiler/assembler should be extracted into its own file, so that it can be properly abstracted. It should get a convenient Python interface so that it can be directly accessed from tests without translation to and from a list-of-tuples representation.

Linked PRs

• gh-117494: extract the Instruction Sequence data structure into a separate file #117496

[encukou]

Since the PR was merged, the wasm32-wasi Non-Debug 3.x buildbot has been consistently failing in test_dynamic.
I can't reproduce the failure locally using .devcontainer.

@ericsnowcurrently, can you reproduce?

[iritkatriel]

Is there something I needed to change in the makefiles for WASI when I added a new source file?