fix(brush size): brush size should be calculated in world not in canvas

[sedghi]

Context

Segmentation Export
Make the generateSegmentation function to return the segmentation dataset instead of the arraybuffer since one might need to push it to the server

Brush Tool
Previously the brush tool modifications/interaction were updating the scalarData and triggering the segmentaion_data_modified A LOT, which is not performance optimized and later when we add the history undo/redo we will end up with problems (since each transaction should be undo/redoable not the whole drag). This PR will show an intermediate step showing the brush locations (similar to volview and 3D Slicer) and when the mouse up happens it does the scalar data update, we call this lazyCalculation

Brush Tool size
Previously the brush tool size was in canvas, which means that when you zoomed in the image the brush size would become smaller which is unexpected by the user. This PR changes it to the world coordinates in mm units

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:

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[jbocce]

Just some minor comments.