SPT: Add Layout Grid block to load for all Atomic sites

[jeryj]

There has been lots of discussion over how to address broken templates in the SPT due to missing blocks. A temporary solution was put in place to remove all broken templates due to missing blocks: #39830

The biggest issue is the missing Layout Grid block. Making that block available should address most of the broken templates, giving us time to come up with a full solution.

Decision for direction from @lessbloat: #40015 (comment)

[github-actions]

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[scruffian]

@jeryj - what is SPT? Shall we close this since we actually want to retire this block now?

[jeryj]

I think it was Starter Page Templates. Yes, let's close!