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[JSC] Nested using blocks lose outer disposals
https://bugs.webkit.org/show_bug.cgi?id=310116

Reviewed by Yusuke Suzuki.

emitUsingBodyScope holds a reference into m_usingScopeStack across the
emitBody call that may recursively append. Once nesting exceeds the
initial Vector capacity, the append reallocates and the stale reference
reads a moved-from UsingScope whose slots vector is empty, so the
finally emits no dispose calls for those outer blocks. ASAN catches the
freed read directly.

Test: JSTests/stress/nested-using-blocks.js

* JSTests/stress/nested-using-blocks.js: Added.
(shouldBe):
(eval.string_appeared_here.string_appeared_here.repeat.depth.1.string_appeared_here.string_appeared_here.repeat):
(shouldBe.async then):
* Source/JavaScriptCore/bytecompiler/BytecodeGenerator.h:

Canonical link: https://commits.webkit.org/309457@main

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