GH-112354: END_FOR instruction to only pop one value.

[markshannon]

In order to support tier 2 side-exits from FOR_ITER variants, we need a target that has the same stack as the exhaustion guard.
Currently we can either jump to the END_FOR, as we do for generators or the instruction afterwards, which we do for FOR_ITER.
In order to exit a guard we need a target in between those instructions, that pops the iterator, but not the value.
The compiler emits END_FOR; POP_TOP instead of END_FOR.
Previously:

 END_FOR (Pops two values) <- FOR_ITEN_GEN targets this
... <- FOR_ITER targets this

Now:

 END_FOR (Pops one value) <- FOR_ITEN_GEN targets this
POP_TOP (Pops one value) <- _GUARD_NOT_EXHAUSTED can target this
... <- FOR_ITER targets this

• Issue: Trace stitching #112354