Add chunk CSS dependency metadata option

[tivac]

Description

Adds a new option, meta, to the rollup plugin that will trigger it to write out a JSON file containing metadata about each JS chunk. Currently it only writes out CSS dependencies, but someday it might do more.

Motivation and Context

Fixes #540

How Has This Been Tested?

Added a test

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[tivac]

Also note the BREAKING CHANGE to bring back common.css in cases where there is CSS that isn't referenced by any JS chunk. Not sure why I thought getting rid of that was a good idea but... I was wrong.

[codecov]

Codecov Report

Merging #542 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #542      +/-   ##
==========================================
+ Coverage   99.16%   99.17%   +<.01%     
==========================================
  Files          41       41              
  Lines         962      970       +8     
  Branches      148      149       +1     
==========================================
+ Hits          954      962       +8     
  Misses          8        8

Impacted Files	Coverage Δ
packages/rollup/rollup.js	100% <100%> (ø)	⬆️

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