nest and path fixup

[esmelusina]

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Purpose of this PR

This change nests the editor folder in preparation for breaking future work down into additional editor assemblies.

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Testing status

Existing automated tests should be all that's necessary.

[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.
Link to Yamato: https://yamato.cds.internal.unity3d.com/jobs/902-Graphics
Search for your PR branch using the sidebar on the left, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

Shader Graph
/.yamato%252Fall-shadergraph.yml%2523PR_ShaderGraph_trunk
Depending on your PR, you may also want
/.yamato%252Fall-shadergraph_builtin_foundation.yml%2523PR_ShaderGraph_BuiltIn_Foundation_trunk
/.yamato%252Fall-shadergraph_builtin_lighting.yml%2523PR_ShaderGraph_BuiltIn_Lighting_trunk

Depending on the scope of your PR, you may need to run more jobs than what has been suggested. Please speak to your lead or a Graphics SDET (#devs-graphics-automation) if you are unsure.

[jessebarker]

LGTM

[jessebarker]

Note to other reviewers (I learned a new git thing today - sorry if this is otherwise well known):

'git show' accepts the command line options for 'git diff'. So, 'git show --diff-filter=r ' means "exclude renames". Very useful when you know that most of your 1700 file PR is just straight renames (there are also options to change what git considers a rename by percentage of difference).