Dynamic Plugins: Deprecation warning building plugin

The following warning is printed when building a plugin:

> DeprecationWarning: Compilation.assets will be frozen in future, all modifications are deprecated.

This appears to be coming from ConsoleRemotePlugin when running with `--trace-deprecation` enabled. I'm building the following plugin:

https://github.com/spadgett/console-customization-plugin

But I suspect it happens with any plugin.

```
yarn run v1.22.15
$ yarn clean && NODE_ENV=production NODE_OPTIONS=--trace-deprecation yarn ts-node node_modules/.bin/webpack
$ rm -rf dist
$ ts-node -O '

' node_modules/.bin/webpack
(node:5651) [DEP_WEBPACK_COMPILATION_ASSETS] DeprecationWarning: Compilation.assets will be frozen in future, all modifications are deprecated.
BREAKING CHANGE: No more changes should happen to Compilation.assets after sealing the Compilation.
Do changes to assets earlier, e. g. in Compilation.hooks.processAssets.
Make sure to select an appropriate stage from Compilation.PROCESS_ASSETS_STAGE_*.
at Compilation.updateAsset (/Users/sam/work/console-customization-plugin/node_modules/webpack/lib/Compilation.js:4241:22)
at /Users/sam/work/console-customization-plugin/node_modules/src/webpack/ConsoleRemotePlugin.ts:81:19
at Hook.eval [as callAsync] (eval at create (/Users/sam/work/console-customization-plugin/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:9:1)
at Hook.CALL_ASYNC_DELEGATE [as _callAsync] (/Users/sam/work/console-customization-plugin/node_modules/tapable/lib/Hook.js:18:14)
at Compiler.emitAssets (/Users/sam/work/console-customization-plugin/node_modules/webpack/lib/Compiler.js:871:19)
at /Users/sam/work/console-customization-plugin/node_modules/webpack/lib/Compiler.js:459:10
at processTicksAndRejections (internal/process/task_queues.js:77:11)
```