Remember related files for Sass on syntax error

[bdukes]

↪️ Pull Request

When watching Sass files, an error from the Sass compiler will cause Parcel to no longer about which files a Sass entry file imports (i.e. which files will cause the entry file to be invalidated). This is documented in #7374 and #9292.

This PR remembers the previous invalidations and reapplies them to the input file in the case of an error.

Presumably this issue also affects other transformers (it's documented to also apply to Pug and Elm, at least), so perhaps this resolution is at the wrong level (maybe should be in RequestTracker?), but it does resolve the problem for Sass in the meantime.

💻 Examples

See #9292

🚨 Test instructions

See #9292

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs
  • For Error recovery from Sass errors #7374
  • For Watcher stops watching dependant scss files after syntax error #9292

[mischnic]

The problem with this approach is that it only works for watch mode and only if you don't restart Parcel while there's a Sass error.

[bdukes]

Certainly it would be better if it worked from a cold-start, but that is out of our control. This workaround approach, however, resolves 99% of the situations where we run into issues.