[backport/v3.x] Make Sprockets::Utils.module_include thread safe on JRuby

[chadlwilson]

Backport/cherrypick of #759 to 3.x

Justification for requesting backport

• Backport seems relatively simple, as this code is large unchanged and module_include appears to be used in the same way on 3.x and 4.x
• The breaking changes in Sprockets 4 (manifest.js and friends) have made migration challenging for some folks (as well as the changes folks needed to get to Rails 6.0/6.1 to even unblock Sprockets upgrade)
• Some wrapping libraries such as Middleman appear to have some challenges with various combinations of sprockets/middleman/sass/sassc versions. Having this particular issue fixed on 3.x sprockets allows some decoupling of these various upgrades without experiencing issues during live reloads as described in cannot load such file -- sass sass/sassc-rails#114 (yes, sassc and sassc-rails are also deprecated, but bridging support to dart sass is available in https://github.com/ntkme/sassc-embedded-shim-ruby)
  • Use of sass-embedded as opposed to sass-rails appears to increase the chance of triggering the concurrency issue this addresses

If this isn't something that will be considered for release, please feel free to note and close this PR 🙏

[chadlwilson]

Closing this given the lack of build automation support for 3.x releases. Since then I have successfully migrated my use case to Sprockets 4.