fix: Start of some changes for image per slice in a volume.

[wayfarer3130]

These are preliminary changes needed for image per slice volume representations.

Context

The changes here aren't active yet, but are a number of related changes to allow lower cost representations of segmentation and imaging data, using single image representations for an entire volume rather than single dataset representations.

Changes & Results

Testing

Checklist

PR

• [] My Pull Request title is descriptive, accurate and follows the semantic-release format and guidelines.

Code

• [] My code has been well-documented (function documentation, inline comments, etc.)

• [] I have run the yarn build:update-api to update the API documentation, and have committed the changes to this PR. (Read more here https://www.cornerstonejs.org/docs/contribute/update-api)

Public Documentation Updates

• [] The documentation page has been updated as necessary for any public API additions or removals.

Tested Environment

• [] "OS:
• [] "Node version:
• [] "Browser: