BridgeJS: Add swift-format-ignore-file to generated Swift sources

BridgeJS: Support nested @js types inside structs and classes

BridgeJS: Diagnose struct initializer parameter order mismatch

Remove @_spi(BridgeJS) from _BridgedAsOptional protocol and its
Optional/JSUndefinedOr conformances so the conformances are visible
in Embedded Swift mode. The underscore-prefixed protocol name already
signals internal API, and all extension methods remain @_spi-gated.

Fixes #689

…lass> (#738)

JSString.Guts previously held a raw JavaScriptObjectRef and released it
unconditionally on whatever thread ran deinit. In the multithreaded Wasm
runtime each thread has its own JSObjectSpace, so releasing a ref on the
wrong thread caused a TypeError crash (BugSnag: rc property of undefined).

JSObject already handles this correctly by capturing ownerTid at init time
and routing deinit through swjs_release_remote when destroyed off-thread.
This change makes Guts hold a JSObject instead of a raw ref, delegating the
correct cross-thread release behaviour to the existing JSObject.deinit path.

Adds a regression test testDeinitJSStringOnDifferentThread that reproduces
the crash deterministically: it forces JS ref allocation on the main thread
via asInternalJSRef(), then drops the last reference on a worker thread.

Fixes the crash seen in v292745-rc4 after upgrading to JavaScriptKit 0.50.2.

https://claude.ai/code/session_01Qhg5GLXZYNJtH63Gs1SwJH

…XtWUJ