Move a few bits from compiler to earlier stages to simplify the compiler

[iritkatriel]

There are validations in compile.c that can move to earlier stages (AST validation or symtable construction).

And the compiler is modifying the symbol table (setting ste_coroutine), which it really shouldn't be doing.

This will simplify the compiler, which is one of the largest code components of the interpreter.

Linked PRs

• gh-121272: move __future__ import validation from compiler to symtable #121273
• gh-121272: compiler no longer modifies the symtable, ste_coroutine always set during symtable construction #121297
• gh-121272: move async for/with validation from compiler to symtable #121361