CSS coverage & warnings on unknown classes

[tivac]

Description

Adds dev.warn and dev.coverage as supported options for @modular-css/css-to-js package, and by extension @modular-css/rollup and @modular-css/vite.

Motivation and Context

dev.warn will cause unknown classes requested from JS to log a warning to the console, instead of the current errors that are thrown.

dev.coverage will cause a global named mcssCoverage to be created which will track accesses of all exported classes per file and allow you to identify unused styles.

How Has This Been Tested?

Added/updated tests

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.
• I have added a changeset for my change.

[changeset-bot]

🦋 Changeset detected

Latest commit: b800294

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
@modular-css/css-to-js	Minor
@modular-css/vite	Minor
@modular-css/rollup	Minor
@modular-css/webpack	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

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