GH-128682: Spill the stack pointer in labels, as well as instructions

[markshannon]

Having automatic insertion and checking of spills in instructions isn't that useful unless we do the same for the rest of the interpreter.
This PR performs spilling and checking on the code in labels as well.

• Adds a single annotation for labels "spilled", to indicate that the code in a label expects the stack pointer to be spilled
• Adds checks that the stack pointer is not used when spilled
• Inserts or checks that the correct spill or reload is inserted when jumping from code with a loaded stack pointer to code with a spilled stack pointer, or vice versa.

• Issue: Consistently spill the evaluation stack when making escaping calls #128682

[markshannon]

The stack_pointer parameter was redundant. In fact, since _PyOptimizer_Optimize escapes, the code generator objects to the use of stack_pointer as an argument when called from the interpreter.