fix: Add prefix to names in a layer

[ChristopherDavisUCI]

This is an attempt to resolve the issues @mattijn raised in #8348 and #8446. (I believe this PR is independent from my other recent PR, #8662.)

I'm very happy to hear comments:

• Is this approach, making sure there are no duplicate names, the correct approach?
• Is this the right place to make the change?
• Is this a reasonable name format (probably not): params.repeaterPrefix + spec.name
• Is there a more natural way to write this logic in JavaScript?

name: spec.name && params.repeaterPrefix ? params.repeaterPrefix + spec.name : undefined

A test is currently failing because of this line:

vega-lite/test/normalize/toplevelselection.test.ts

Line 89 in 4556109

expect(normalized.concat[0].layer[0].name).toBe('a');

Is it correct to have both normalized.concat[0].layer[0].name and normalized.concat[1].layer[0].name equal to "a"? This PR would change that, so it would break this test.

Thanks again for any comments!

[ChristopherDavisUCI]

Hi @domoritz, thanks for the reviews of my other PRs. I changed this one to "ready for review" also, although please see my many questions in the original comment above.

[domoritz]

This will remove the name when there is no repeater prefix, which is definitely wrong (see changed example in this diff).

[ChristopherDavisUCI]

Thanks @domoritz for proposing the fix in #8733! I will close this, but please let me know if I misunderstood anything.