add `experiments.backCompat: false` (default in `experiments.futureDefaults`)
remove unused `experiments.asset`
enable `experiments.topLevelAwait` and `experiments.asyncWebAssembly` by default in `experiments.futureDefaults`
deprecate writing to compilation.assets after sealing.
merge all asset processing into single hook with stages.
Deprecate additionalChunkAssets and optimizeChunkAssets.
Redirect additionalAssets, optimizeAssets to processAssets for backward-compat.
Remove finishAssets hook without deprecation as it was not in v4.