I've pulled this out of#118116.

Basically, I've turned most of_PyImport_LoadDynamicModuleWithSpec() into two new functions (_PyImport_GetModInitFunc() and_PyImport_RunModInitFunc()) and moved the rest of it out into_imp_create_dynamic_impl(). There shouldn't be any changes in behavior.

This change makes some future changes simpler. This is particularly relevant to potentially calling each module init function in the main interpreter first. Thus the critical part of the PR is the addition of_PyImport_RunModInitFunc(), which is strictly focused on running the init func and validating the result. A later PR will take it a step farther by capturing error information rather than raising exceptions.

FWIW, this change also helps readers by clarifying a bit more about what happens when an extension/builtin module is imported.

• Issue:Single-Phase Init Extension Module Init Functions Still Run in Isolated Interpreters #117953