Reduce padding in `_jl_handler_t` (#61662)
Reorder fields in `_jl_handler_t` so that 8-byte fields come first,
followed by the 4-byte `defer_signal` and 1-byte `gc_state` at the tail.
This eliminates 8 bytes of padding, as `_jl_handler_t` is 8-byte-aligned
and is the most flexible layout for future extensions. I haven't seen
any disadvantages with the new order, but there might be internals that
I don't know about.
Exception contexts are probably not the most pressing issues in terms of
memory usage, but that does not mean that we should waste memory.
The problem was found by Claude Opus 4.7.
Co-authored-by: Patrick Häcker <patrick.haecker@bosch.com>
