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

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