[editor] Handle selection history in Shader Graph and VFX Graph (WIP)

[aras-p]

Purpose of this PR

I'm implementing "selection history" for the editor as a whole, and while it handles "things that participate in Selection C# API" (game objects & assets) out of the box, the shader & vfx graph selections are neither assets nor game objects. So this implements support for selection history for these graph views, so that the new back/forward buttons would work nicely as a user would expect them to.

This will require https://github.cds.internal.unity3d.com/unity/unity/pull/7194 to land first in the "main" editor codebase, and as such this PR is WIP/draft for now.

Testing status

TBD

Comments to reviewers

TBD

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
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Shader Graph
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[julienf-unity]

Not sure what's the status of this PR now that Aras left?

[julienf-unity]

@julienamsellem Is it something that we should consider merging?

[aras-p]

@julienf-unity this PR first needs the unity main codebase side PR (that adds newly needed Selection APIs) to land first. I don't know if it landed yet :) But, talk with Marius Zrelskis on Slack -- I've left up to him to land both the code side PR, and this one.

[julienamsellem]

This PR is depends on another PR on the editor which is not merged yet. So until this dependency is merged we cannot merge.
But at least we can test it and see if it works fine with latest changes.

[julienf-unity]

Ok just wanted to make sure this wasnt some work for nothing. Looks like this PR will have to be migrated for srp2core2 then