fix: support deferred imports introduced by hot updates - #16015

Motivation

Fixes #15960.

With experiments.deferImport, lazy compilation can introduce deferred imports through a hot update after the initial bootstrap has run. The deferred namespace and async-dependency helpers access the module cache through a bootstrap-local variable, causing ReferenceError: __webpack_module_cache__ is not defined in the hot-update chunk. The deferred exports table has the same scope problem, and the initial require may not include support for sharing those exports.

Changes

Reference the module cache through MODULE_CACHE and expose the deferred exports table as DEFERRED_MODULE_EXPORTS. When HMR and experiments.deferImport are enabled, initialize the shared table and the corresponding require support in the initial bootstrap, while generating the deferred namespace helper only when needed.

Carry the shared state through both runtime modes and modern-module output so pending namespaces retain their export targets when helpers are updated. Also remove table entries after successful module execution with strictModuleErrorHandling, preventing stale export objects from being reused by subsequent hot updates.