[ic-checkbox] - indeterminate checkbox styling incorrect

[ad9242]

Summary of the bug

There are some styling issue which the indeterminate checkbox

🪜 How to reproduce

The styling is different, between the built component & the designs

Built Component:

Figma design:

Need to decide which is correct and ensure they match.

Also requires a fix in the built component as a disabled and indeterminate checkbox has a blue line: However, fixing the styling of this will depend on the outcome of aligning the component with figma

[MI6-255]

Design to review which we will go with

[mi6-577]

Filled with white dash (as per figma) is how other design systems (eg Material Design) handles indeterminate checkbox states. Therefore this will require a dev change, rather than design

[MI6-286]

Issue no longer relevant - styling matches designs.