Add source-hash plugin

[jhildenbiddle]

Awesome Contribution Checklist:

• [x] I have read, and re-read the Contributing Guidelines
• [x] I have searched to ensure the suggested item doesn't exist on this list
• [x] This PR contains only one item

Please Provide a Link A Repository for Your Addition

https://github.com/jhildenbiddle/rollup-plugin-source-hash

Please Describe Your Addition

See Why? section of plugin documentation for details.

Note: This plugin provides an enhanced version of the following feature request: https://github.com/rollup/rollup/issues/4931