[ORL-72] Add support for de-duplicating tags

[orels1]

Currently it is possible to define duplicate tags, e.g.

Tags {
  "RenderType" = "Opaque" "RenderType" = "Transparent"
}

While this doesn't cause issues for regular rendering - unity picks the last instance of the tag, it can cause issues with shader replacement and bakery, so duplicate tags should deduplicated and only the last instance should be set in the template

De-duplication should be done using the ShaderParser

_{From SyncLinear.com | ORL-72}