Expose Light2D properties for scripts - Shape properties, falloff intensity

[kennytann]

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Purpose of this PR

Why is this PR needed, what hard problem is it solving/fixing?

Adds public api for shape path in Light2D which allows users to set their own custom shapes for freeform lights.
Updated docs to reflect the changes.

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Testing status

Describe what manual/automated tests were performed for this PR

Open UniversalGraphicsTest_2D project from graphics repo.
Open TestRunner.
Select PlayMode tab.
Run 2 tests "CachedMeshDataIsOverriddenByRuntimeChanges" and "CachedMeshDataIsUpdatedOnChange".
Ensure the tests are successful.

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Comments to reviewers

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[github-actions]

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[ernestasKupciunas]

Approving without testing. Good job with the testing coverage!

[BoonKiangTan]

Fix verified on branch:

Version: 2022.1.0a10.1326
Revision: trunk 48c8cfa2acec
Built: Fri, 17 Sep 2021 07:51:06 GMT
Package branch: 2d/public-api-light2d-shape-path (8543fa5)

• Verified changed public API "shapeLightFalloffSize" , "SetShapePath" and "falloffIntensity" work as intended
  

• Verified added "CachedMeshDataIsOverriddenByRuntimeChanges" and "CachedMeshDataIsUpdatedOnChange" tests pass
  

• Verified summary API description displays correctly