This disables the auto-reinit functionality of aborts with --experimental-reset-state-function to instead require an explicit call to the schedule_reinit() function. In addition, any use of schedule_reinit() will automatically bring in the reinit machinery by treating it as an intrinsic.

schedule_reinit() sets a private JS-side flag instead of writing to a __instance_terminated sentinel value. This means:

• schedule_reinit() can be called during normal execution without triggering a trap — the current call completes normally and the reset happens on the next export call
• the abort-then-reinit path still works: the abort hook fires, calls schedule_reinit(), and the guard resets instead of throwing
• __instance_terminated is a clean boolean (0 = live, 1 = terminated) with no internal sentinel values leaked into the public spec

Usage for abort on reinit:

fn on_abort() {
    wasm_bindgen::handler::schedule_reinit();
}

#[wasm_bindgen(start)]
fn start() {
    wasm_bindgen::handler::set_on_abort(on_abort);
    wasm_bindgen::handler::set_on_reinit(on_reinit);
}

A new guide section is added "Handling Aborts" covering these behaviours as a separate guide page to "Catching Panics".

What changed:

• renamed reinit() to schedule_reinit() to reflect that it schedules reinitialization for the next export call
• __wbindgen_reinit intrinsic now sets a JS variable (__wbg_reinit_scheduled) instead of writing -1 to linear memory
• __wbg_handle_catch unconditionally writes 1 (no conditional to preserve a sentinel)
• __wbg_reset_state only references __wbg_called_abort / __wbg_reinit_scheduled when the catch handler machinery is active, fixing a ReferenceError on panic=abort builds with --experimental-reset-state-function
• auto-detection of schedule_reinit() usage emits private reinit machinery without --experimental-reset-state-function
• updated guide: __instance_terminated documented as boolean, schedule_reinit docs note it works outside abort context
• remove on_reinit for now, now that we support multiple start functions instead

Test coverage: termination, termination_abort_handler, termination_reset_state, termination_reinit, and termination_reinit_auto_detect all pass.