CVE-2025-12429: Inappropriate implementation in V8

The upstream fix for a recently reported security issue caused regressions
in the LTS branches of Chromium. To mitigate the risk, this patch
reverts the change that enabled the feature that contains the security bug.

Manual revert of patch originally reviewed on
https://chromium-review.googlesource.com/c/v8/v8/+/4521712:
[interpreter] Enable TDZ elision by default

Bug: v8:13723
Change-Id: I003bbb2b6b5eb58837cb35e1db088218ed9b6d3c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4521712
Commit-Queue: Shu-yu Guo <[email protected]>
Reviewed-by: Toon Verwaest <[email protected]>
Cr-Commit-Position: refs/heads/main@{#87775}
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/687659
Reviewed-by: Michal Klocek <[email protected]>
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/689571

Author: mibrunin

chromium/v8/src/flags/flag-definitions.h

@@ -1004,8 +1004,9 @@ DEFINE_BOOL(ignition_filter_expression_positions, true,
 DEFINE_BOOL(ignition_share_named_property_feedback, true,
             "share feedback slots when loading the same named property from "
             "the same object")
-DEFINE_BOOL(ignition_elide_redundant_tdz_checks, true,
+DEFINE_BOOL(ignition_elide_redundant_tdz_checks, false,
             "elide TDZ checks dominated by other TDZ checks")
+DEFINE_WEAK_IMPLICATION(future, ignition_elide_redundant_tdz_checks)
 DEFINE_BOOL(print_bytecode, false,
             "print bytecode generated by ignition interpreter")
 DEFINE_BOOL(enable_lazy_source_positions, V8_LAZY_SOURCE_POSITIONS_BOOL,