fix: fix hmr for platform specific files in linked plugins

[Fatme]

Currently hmr for platform specific files in linked plugins work only in intervals of 60 seconds. This is due to the fact that CachedInputFileSystem of webpack has a cache that is invalidated on every 60seconds. We used ExtaWatchPlugin in order to add platform specific files to the webpack's compilation. This plugin doesn't follow symlinks and this led to the different problems when applying changes from platform specific files. So we decided to remove it and to override correctly watch's file system from webpack. We have a logic for overriding webpack's watchFileSystem but this logic doesn't work as it seems it is not compatible with webpack v4.0.

Currently compiler.watchFileSystem.watch has 2 callbacks - callback and callbackUndelayed. The callbackUndelayed is executed on every file's change as we can see here. We override this callback and purge the file's cache on callbackUndelayed. This way we ensure the cache is invalided for the changed file and hmr after that will work.

Rel to: #942

PR Checklist

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What is the current behavior?

hmr doesn't work for platform specific files in linked plugins.

What is the new behavior?

hmr works for platform specific files in linked plugins.

Fixes/Implements/Closes #[Issue Number].