[perl #43425] local $[: fix scoping during parser error handling.

 [perl #43425] local $[: fix scoping during parser error handling.

 Change 22306# inadvertently made 'local $[' statement-scoped
 rather than block-scoped; so revert that change and add a
 different fix. The problem was to ensure that the savestack got
 popped correctly while popping errored tokens. We how record the
 current value of PL_savestack_ix with each pushed parser state.

p4raw-id: //depot/perl@31615