Shader Graph Updates and Fixes

[Cameron-Micka]

Overview

• Fixed a bug where source and destination blend alpha were not maintained when "Allow Material override" was checked.
• Fixed a Unity 2021 shader compilation error.
• Acrylic bug fix, UNITY_UV_STARTS_AT_TOP is always defined, so the previous check was incorrect. unity_OrthoParams.w was just another way to check if the UV was flipped. So, simplifying the check.
• @vmoras6699 changed the scalable shader graph target's unlit low shader path to use baked lit.

Verification

As a reviewer, it is possible to check out this change locally by using the following
commands (substituting {PR_ID} with the ID of this pull request):

git fetch origin pull/{PR_ID}/head:name_of_local_branch

git checkout name_of_local_branch