Flexilayouts follow up: UUIDs shown instead of region names in `/admin/reports/blocks`

[klonos]

In /admin/reports/blocks layouts that use flexible templates return cryptic UUIDs as region names:

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PR by @klonos: backdrop/backdrop#2925

[jenlampton]

We should be able to switch to the human-readable name for each region here pretty easily. I don't think it's related to #4045.

[stpaultim]

PR works for me as it is, however I see that @quicksketch has made some requests for changes to the code. Am a little confused about the last comment by @jenlampton. I think the PR does this?

[klonos]

Thanks for testing this out @stpaultim 👍 ...that PR was coming from a mis-named branch, so I have replaced it with backdrop/backdrop#2925, in which I have also addressed @quicksketch's comment from the previous PR.

Ready for another run ...nothing should have changed functionality-wise, so only code review really; but wouldn't mind re-testing.