Feature/unity 1451 shader unification

[MattGrayUL]

Contributor Tasks

• Create or edit test cases here
• Add a CHANGELOG entry for this change.
• Ensure documentation requirements are met e.g., public API is commented.
• Consider any licensing/other legal implications for this MR e.g. notices required by any new libraries.

Test Cycle

Link to the test cycle here.

Reviewer Tasks

• Code reviewed.
• Non-code assets e.g. Unity assets/scenes reviewed.
• All tests must be ran and cover all scenarios (If not, add new tests to the cycle and run them).
• Documentation has been reviewed.
• Approve with a comment of any additional tests run or any observations.

Related JIRA Issues

Closes UNITY-1451 & UNITY-936